anthropic/claude-opus-5
google/gemini-3.1-pro-preview
perplexity/sonar-pro## The framing I'd push back on before any arithmetic
The question as posed — "can a 22 kW start a 104 A locked-rotor compressor?" — is the question the generator industry has trained homeowners to ask, and it is the wrong one. I'll show below that 104 A is trivially within a 22 kW standby's capability, with a margin so large it isn't worth a second thought. The genuine sizing risk in this house is somewhere else entirely, and it's hiding inside the same piece of equipment he's worried about: a 4-ton geothermal unit in a mostly-electric house almost certainly has an **electric auxiliary / emergency heat package** of 5, 10, 15, or 20 kW bolted to it. Fifteen kW of strip heat is 62.5 A at 240 V — that is roughly *six times* the continuous burden of the 104 A inrush and it lasts for hours, not milliseconds. That, not the compressor, is what decides whether 22 kW is right.
Two housekeeping notes on his assumptions first, since he asked me to flag errors:
- **240 V single-phase: correct, keep it.**
- **81 A NG / 92 A LP: correct and self-consistent.** 19,500 ÷ 240 = 81.25 A; 22,000 ÷ 240 = 91.67 A. Note Generac's own caveat that maximum kVA and current are limited by fuel BTU content, ambient temperature, altitude and engine condition, and that maximum power decreases roughly 3.5% per 1,000 ft of elevation and about 1% per 10 °F above the reference temperature. So those two numbers are *ceiling* numbers at sea level on a cool day, not design numbers.
- **One assumption he didn't make but should:** his TEV49 is a ClimateMaster **Tranquility 30 (TE) Digital**, vertical, 4-ton — a two-stage compressor with a variable-speed fan and vFlow variable water flow. This matters in three ways I'll use below.
---
## 1(a) — Can a 22 kW *start* 104 A of locked rotor? Yes, and not narrowly.
### The unit-conversion that dissolves the problem
The mistake almost everyone makes is comparing an **ampere** number to a **kilowatt** number as if they were the same currency. They are not. Let me do both conversions explicitly.
**Apparent power at the instant of start:**
> 104 A × 240 V = **24,960 VA = 25.0 kVA**
That looks alarming next to "22 kW." It shouldn't, because locked rotor current is almost entirely *reactive* — magnetizing current in what is electrically a shorted transformer. At the first instant the rotor is at standstill, an induction motor behaves like a short-circuited transformer, which is why the peak is called locked rotor amps, and LRA typically runs 3 to 8 times full-load amps — but this does not equate to 3-8× the real power, because a starting motor's power factor is low (under 0.5).
**Real power the engine actually has to make**, at a locked-rotor power factor of ~0.30–0.40:
> 25.0 kVA × 0.35 ≈ **8.8 kW**
That's the number the 999 cc engine sees. Not 25 kW. **Under 9 kW, for well under a second.** The engine has 22 kW of capability and a governor that will tolerate transient droop well past that.
**Apparent power the alternator actually has to make**, once you allow the voltage sag that every motor start produces (and which motors tolerate fine — they just take a bit longer to accelerate):
> At a 15% dip allowance: (104 × 0.85) × (240 × 0.85) = 88.4 A × 204 V = **18.0 kVA**
> At a 30% dip allowance: (104 × 0.70) × (240 × 0.70) = 72.8 A × 168 V = **12.2 kVA**
This is the standard method — a typical 5-ton A/C at 145 LRA/240 V requires (145×0.7)×(240×0.7) = 17,052 VA to start at a 30% dip, which does not mean you need a 17 kW machine, only one that can supply that much surge; commercial practice allowing only 15% dip gives 0.85×0.85 = 0.72 of nominal starting kVA. His compressor is *smaller* than that textbook example. It needs 12–18 kVA of momentary surge from a machine rated ~22 kVA continuous.
### The ratio test
| Fuel | Continuous A | LRA ÷ continuous A |
|---|---|---|
| Natural gas (19.5 kW) | 81.25 A | 104 / 81.25 = **1.28×** |
| LP (22 kW) | 91.67 A | 104 / 91.67 = **1.13×** |
Standby alternators are routinely good for **2.5–3× rated current momentarily** with a voltage dip. He needs **1.13–1.28×**. This is not a close call. A 104 A LRA would be comfortable on a 14 kW unit (58 A → 1.8×) and probably on an 11 kW.
**Sanity check on his own number:** at LRA/RLA ≈ 5–6 for a scroll, 104 LRA back-solves to a running load of **17–21 A**, i.e. ~4.1–5.0 kW of compressor. That is exactly right for a 4-ton geothermal compressor, so his 104 A figure is credible and internally consistent. Good — his data is trustworthy; his worry is misdirected.
### The Generac figure I will *not* invent
He asked for honesty here, so: **I cannot verify a published Generac "motor starting" or "maximum surge kVA" number for the 22 kW air-cooled unit.** I've seen the spec sheet's maximum-rating disclaimer but not a motor-starting row I'd stake the answer on, and I'm aware the air-cooled spec sheet now spans a family that includes a Power Extender Kit across 22–28 kW, so model-specific numbers shift. **What to ask for by name:** (i) the "Motor Starting" / "Max. Motor Starting kVA" row on the spec sheet for his exact model, and (ii) a printout of the dealer's **Generac Power Design Pro** sizing report, which does this calculation with his actual load list. If a dealer tells you 22 kW is *required* to start a 104 A compressor, he is either selling up or repeating folklore — and you'll find that exact folklore all over the internet, e.g. a homeowner with a 109 LRA Trane told by one Generac installer that anything under 22 kW "will in time ruin your A/C motor," and by another that 16 kW would be fine. The second installer was right on the starting question.
## 1(b) — Can it *carry* the running load? This is the binding constraint. Here's the method.
Let **L** = his simultaneous running amps at 240 V, with the geo running, *one* of oven/dryer, and no strip heat.
**Step 1 — design ceiling.** Use 80% of continuous as the comfort target for a machine that may run for days:
> NG: 0.80 × 81.25 = **65 A** (≈ 15.6 kW)
> LP: 0.80 × 91.67 = **73 A** (≈ 17.6 kW)
If he's on natural gas, **design to 65 A.** The NG derate is ~11% and it is permanent, not a bad-day allowance.
**Step 2 — step-load check.** Worst instant = L + 104 A (compressor cycles on while everything else is running):
> LP, 2.5× momentary limit: 2.5 × 91.67 = 229 A → L could be as high as **125 A** before starting becomes the limiter
> NG, 2.5×: 2.5 × 81.25 = 203 A → L up to **99 A**
**Step 3 — compare.** 65 A (continuous limit) vs 99 A (starting limit). **The continuous rating binds first, by a wide margin.** Every dollar and every worry should go to Step 1. This is the whole answer to question 1.
**Illustrative** worksheet (these are my placeholders, *not* his numbers — he must replace them from nameplates):
| Load | 240 V amps |
|---|---|
| Geo unit total, compressor + ECM blower + vFlow pumps (nameplate MCA *minus* heat) | ~25 |
| Electric water heater, 4.5 kW | 18.8 |
| Well pump, 1 hp, running | ~9 |
| Refrigerator + freezer | ~3 |
| Lights, plugs, electronics, network, sump | ~12 |
| **Base subtotal** | **~68** |
| + electric dryer (5.7 kW) | +24 → 92 |
| + electric range/oven | +30–40 → 98–108 |
Note what that illustration shows: the *base* already nudges past 65 A on natural gas, and **either** big appliance blows through 81 A. That is not a reason to buy a bigger generator — it's a reason to configure automatic load management, which brings me to the thing he actually asked for without realizing it.
### The reframe he needs: "load shedding" ≠ "unplugging things"
He said he doesn't want to unplug things or load-shed. Those are two different wishes, and only the first one is worth paying for. Generac's transfer switches offer built-in HVAC energy management, and an auxiliary transfer switch contact kit lets the switch lock out a single large electrical load that may not be needed; Smart Management Modules do the same per-circuit. Put modules on the range and the dryer and they take turns **automatically, in milliseconds, with him touching nothing.** From the kitchen, that is indistinguishable from an infinitely large generator — except on the rare occasion he tries to bake and dry simultaneously, which he already told us he doesn't need. A few hundred dollars of load management buys the "don't touch anything" experience far more cheaply than upsizing the machine.
---
## 2 — Does a soft starter change the picture? It de-risks. It does not resize.
**How much it cuts LRA:** the vendor claim for a SureStart-type device is a reduction in locked-rotor draw of up to 60%, with a field example where a 62 A nameplate LRA was reduced to 25 A, after which an 11 kW generator "didn't even notice" the A/C starting. Applied to his number:
> 104 A × (1 − 0.55) ≈ **47 A**, plausible band **35–52 A**
> New ratio on NG: 47 / 81.25 = **0.58×** — below the generator's continuous rating. The start becomes electrically invisible.
**Typical cost:** the device itself generally runs in the **$400–700** range and installed **$700–1,300** depending on labor and whether the tech is already in the cabinet. Treat that as a market estimate, not a quote — get the number from his HVAC contractor, and note this is HVAC labor, not the generator installer's.
**My verdict, and it diverges from the usual advice: buying a soft starter to enable a smaller generator would be a mistake in this house.** The logic is Step 3 above. Because his constraint is *continuous* load, not *starting* load, a soft starter buys him **zero kilowatts of carrying capacity.** Cutting 104 A to 47 A for 0.4 seconds does nothing for the 65–75 A he must carry for three days. The scenario in that forum post — an 11 kW unit rescued by a soft start — is an *air-conditioning* house where the A/C is the only real load. His is a *mostly-electric* house where the A/C is one of six real loads.
So the soft starter is legitimately worth considering, but for the right reasons: it eliminates light flicker and voltage dip on every start (utility power included, 5,000+ starts a year), and it reduces mechanical and thermal stress on a compressor that is expensive to replace. Those are real. "It lets me buy an 18 kW instead of a 22 kW" is not.
**Two caveats specific to his machine:**
- **Get OEM blessing before field-adding one.** ClimateMaster clearly endorses the concept — their current Tranquility 30 SE offers an optional factory-installed compressor soft starter to reduce inrush currents for more efficient startups, alongside EC blower motors with integrated soft start. But *factory-approved on a new SE* is not the same as *third-party retrofit on a TE without voiding a compressor warranty.* Ask ClimateMaster in writing, or ask whether a factory soft-start kit exists for the TE.
- **Don't expect the two-stage compressor to soft-start itself.** A two-stage scroll unloads *capacity* via a solenoid but it is the same motor with the same rotor; my understanding is the starting inrush is essentially unchanged between stages. Worth confirming with ClimateMaster, but plan on 104 A being the real number regardless of which stage calls. What the TE *does* already give him is a variable-speed ECM blower that soft-starts on its own — meaning **the compressor is the only hard start in that cabinet**, and he's already identified it.
---
## 3 — The flip conditions, as thresholds he can go check
### 22 kW is TOO SMALL if any of these is true
**T1 — The one that matters most: electric auxiliary/emergency heat.**
Find the geo unit's **electric heat package kW** (in the model nomenclature and on the nameplate as a second MCA row, often "unit amps with electric heat"). Convert: kW × 1000 ÷ 240 = amps.
> 5 kW = 20.8 A · 10 kW = 41.7 A · 15 kW = **62.5 A** · 20 kW = **83.3 A**
**Threshold: if [geo MCA including electric heat] + [rest of base load] > 81 A (NG) or 92 A (LP), and the strips are not locked out during generator operation, 22 kW is undersized.** A 15 kW strip package alone consumes 77% of the NG rating. This is the scenario where he loses power on a February night, the geo throws an alarm or the thermostat calls emergency heat, 62.5 A of resistance heat slams on, and the generator overloads or nuisance-trips. **The fix is usually not a bigger generator — it's a relay that locks out aux/emergency heat whenever the generator is the source.** The geo will still heat the house on compressor-only; it will just recover from setback slowly. Note that this is a known pain point: a ClimateMaster TE 30 owner on a generator forum was specifically trying to figure out the best way to reduce the start load or lock out the geothermal system, and reported that ClimateMaster hadn't been able to help. Get it answered *before* signing, in writing, as a scope item for the installer.
**T2 — Base load exceeds the design ceiling.** If L (geo running, one big appliance, no strips) **> 65 A on NG / > 73 A on LP**, he needs load management at minimum, and a larger unit if the load can't be managed.
**T3 — Concurrent starts.** If the well pump, a second geo unit, or a second compressor can start *in the same instant* as the geo compressor, add their LRAs: 104 + (well pump LRA, often 40–60 A) = 145–165 A. Still under 2.5× on LP, tighter on NG. Worth a look only if T1 and T2 pass.
**T4 — The one I'll bet the rest of the council misses: gas supply capacity.** He mentioned the **gas regulator** in the same breath as the meter. A 22 kW air-cooled unit at full load consumes on the order of 300 cubic feet per hour of natural gas — confirm the exact figure from the spec sheet rather than trusting mine. **Threshold: is his utility meter and regulator rated for [existing appliance total CFH] + [generator CFH] simultaneously, at the required inlet pressure at the generator under full flow?** A standard residential meter shared with a furnace, water heater and range can be right at the edge. A gas-starved generator doesn't announce itself with an overload light — it sags under load, hunts, and drops out precisely when the compressor kicks in, which the homeowner then misdiagnoses as "the generator is too small." **Sizing a generator includes sizing its fuel supply.** An undersized meter is a utility upgrade request, sometimes free, sometimes not, and sometimes weeks of lead time. Ask now.
**T5 — Derates.** Elevation and heat. At 4,000 ft: 19.5 kW × (1 − 0.14) ≈ 16.8 kW = **70 A** on NG, which drops the 80% design ceiling to 56 A. If he's at altitude, recompute everything with the derated number — roughly 3.5% per 1,000 ft.
### 22 kW is MORE than he needs if
**T6 — L < ~45 A (≈11 kW)** with strips locked out and load management on the range and dryer. An 18 kW (75 A) would carry that and start 104 A at 1.39×; even a 14 kW (58 A) starts it at 1.8×.
But here's my honest asymmetry argument, and it cuts against downsizing. Air-cooled *gaseous-fuel* engines do not wet-stack the way lightly loaded diesels do, so **oversizing a natural-gas standby is a low-consequence error** — you pay a bit more up front and burn marginally more fuel. Undersizing is a high-consequence error: nuisance trips in an ice storm, or a rip-out. The old "don't oversize a generator" advice is diesel advice, imported into the gas standby world where it doesn't really apply. Given that, **if his numbers land anywhere near the middle of the range, 22 kW is the right call and he should stop optimizing.** I'll add one correction to a claim I'd have made a couple of years ago: 22 kW is no longer the last stop before the liquid-cooled price cliff — Generac's air-cooled spec sheet now covers a **22–28 kW** range, so if T1 or T2 fails, his next step is likely a 26 or 28 kW air-cooled rather than a jump to liquid-cooled. That makes upsizing cheaper than it used to be and slightly weakens the "buy the biggest air-cooled just in case" reflex.
---
## 4 — Bottom line, plain language
Your 104-amp compressor surge is a non-problem. It lasts a fraction of a second, it's mostly reactive current that barely loads the engine — the engine only sees about 9 kW of real power during the start — and at 104 amps against the generator's 81 (natural gas) or 92 (propane) continuous amps, you're asking for only 1.1 to 1.3 times its rating when standby units handle 2.5 times routinely. Any installer who says you need 22 kW *to start the compressor* is arguing from folklore. What actually decides whether 22 kW is right is the boring number nobody quoted you: the total amps you'll be **carrying** for three days straight. Design to 65 amps on natural gas or 73 on propane, and understand that the hidden monster is your geothermal unit's electric backup heat strips — if that package is 10 or 15 kW and it can turn on while you're on generator, it will eat two-thirds of the machine by itself and no reasonable generator will save you. Lock the strips out when you're on generator power, put automatic load-management modules on the range and the dryer (that is *not* "unplugging things" — it's invisible and automatic), and 22 kW is very likely correct. Skip the soft starter as a sizing tool; consider it separately as a flicker-and-longevity upgrade if you like it on its own merits.
### Pull or confirm these five things before you sign
1. **From the ClimateMaster nameplate and spec sheet (TEV049, Tranquility 30 TE):** the **electric heat package kW**, and both MCA ratings — with and without electric heat. Also confirm the compressor's RLA (should be ~17–21 A if 104 LRA is right) and the amp draw of the ECM blower and vFlow loop pumps. *This single item determines the answer.*
2. **In writing from the generator installer:** how aux/emergency electric heat will be **locked out during generator operation** — which relay, wired to what, who installs it, at what cost. Get it in the scope of work, not in a verbal assurance. And confirm the load-management modules and which circuits they're on.
3. **Your fuel and your gas meter.** State whether you're on natural gas or propane (it's an 11% capacity swing and changes your design ceiling from 65 to 73 A). If natural gas, ask the installer to confirm the **meter and regulator CFH capacity** covers the generator *plus* all existing gas appliances at full flow, and whether a utility meter upgrade is required. Get this answer early — it's the long-lead item.
4. **A one-page load list you build yourself**, walking the panel breaker by breaker: for each circuit you want live during an outage, write the nameplate amps, and total it. Bring it to the installer and ask for the **Generac Power Design Pro sizing report** built from *your* list, plus the **"Motor Starting" row** off the spec sheet for your exact model. If he can't or won't produce either, that tells you something about the quality of the sizing behind the quote.
5. **Your elevation**, if you're above ~2,000 ft — and then redo the ceiling arithmetic with the derate applied.
Here is the sizing-and-configuration analysis for your situation.
### 1. The Two Distinct Problems: Starting vs. Running
**The Starting Problem (Inrush):**
When a compressor motor starts, there is a momentary surge of power called Locked Rotor Amps (LRA) that lasts less than a second. Your ClimateMaster’s 104 A LRA means it demands 24,960 watts (104 A × 240 V = ~25 kVA) for a fraction of a second.
A 22 kW Generac (which produces 22 kVA continuously on propane, or ~19.5 kVA on natural gas) typically has a maximum motor-starting capacity of around 35 to 40 kVA (the exact figure varies by model year, but this is the standard envelope before the voltage dips too low).
*Is 104 A a problem?* Yes. If your heat pump tries to start while you are already running an electric water heater (typically 4,500 W / ~19 A) and an electric dryer (typically 5,500 W / ~23 A), the baseline house load is already ~42 A. Adding a 104 A surge on top spikes the immediate demand to 146 A (~35 kVA). This pushes the generator right to the edge of stalling or tripping its breaker. Because you explicitly stated you do **not** want to use load-shedding modules (which automatically lock out other appliances when the heat pump starts), the 104 A surge is a massive risk.
**The Running Problem (Continuous):**
Once the heat pump is running, it drops from its 104 A starting surge to its Running Load Amps (RLA)—likely somewhere around 15–20 A for a unit of that size. The generator's continuous rating (81 A on Natural Gas, 92 A on Propane) must be larger than the sum of every appliance running at the same time.
### 2. The Soft Starter: A Mandatory Linchpin
A soft starter (like a Micro-Air EasyStart) uses a microprocessor to ramp up the compressor slowly, drastically reducing the inrush current.
* **The Reduction:** It typically cuts LRA by 65–70%. Your 104 A surge would drop to roughly 30–35 A.
* **The Cost:** The device costs about $300–$400, plus an hour or two of labor to install inside the heat pump (total ~$500–$700).
* **The Impact:** For your specific goal of an all-electric house *without* load-shedding, a soft starter is not an optional upgrade; it is practically mandatory. It takes the starting surge off the table entirely, de-risking the 22 kW unit. If you install one, you only have to worry about sizing for your continuous running load, which might even allow you to drop to an 18 kW generator depending on the math.
### 3. The Flip Condition: When 22 kW is the WRONG Size
Here is the exact threshold to check to know if 22 kW is wrong.
Let **L** equal the sum of the running amps of your heat pump, electric water heater, well pump (if applicable), refrigerator, lights/outlets, and *one* of the two large appliances (either the dryer OR the oven, since you won't run both).
* **It is TOO SMALL if:** **L** is greater than 81 Amps (if you are on natural gas) or 92 Amps (if you are on propane). If your simultaneous continuous load exceeds this, the main breaker on the generator will trip and the power will go out.
* **It is TOO BIG if:** You install a soft starter (dropping the surge to ~35 A) AND your calculated **L** is consistently under 60 Amps. In this scenario, you are overspending on a 22 kW unit and the higher fuel consumption it requires; a 14 kW or 18 kW generator would serve you perfectly.
### 4. Bottom Line and Next Steps
**Bottom Line:** A 22 kW generator is right on the edge of failing to start your geothermal heat pump if other heavy electric appliances are running. Because you do not want to use automated load-shedding modules, you should strongly mandate a soft starter for the heat pump; doing so guarantees the generator won't stall on startup, leaving you with the simple task of making sure your total running appliances don't exceed the generator's continuous limit.
**Before you sign, confirm these three things:**
1. **Your Fuel Type:** Check whether you have Natural Gas or Propane. The generator loses about 11% of its power on Natural Gas (giving you 81 A instead of 92 A).
2. **The Heat Pump's RLA:** Look at the spec plate on the ClimateMaster and find the "RLA" (Running Load Amps). You need this number to calculate your continuous load.
3. **Your Peak Continuous Load:** Add up the running amps of your heat pump (RLA), water heater, and oven. If that number gets dangerously close to 81 A (NG) or 92 A (Propane), you need a bigger generator (liquid-cooled) or you must accept some form of automated load management.
I’ll treat this as a sizing and configuration problem, with the two key questions separated: **can the generator start the geo compressor**, and **can it carry everything he wants running at once**.
I’ll stay away from brand/price, focus on physics and arithmetic, and point out where Generac-specific data would be needed but isn’t available in the search results.
---
## 1. Two distinct problems: START vs CARRY
### 1a. Can a 22 kW unit START a 104 A locked‑rotor compressor?
**Assumptions given:**
- 240 V, single‑phase residential service.
- Geothermal compressor locked‑rotor current (LRA) ≈ **104 A at 240 V**.
- Generator nameplate: **22 kW standby**.
- Continuous output (from your assumption, not a spec sheet):
- ~81 A on natural gas at 240 V
- ~92 A on propane at 240 V
**Step 1: Translate 104 A LRA into power/kVA demand**
Locked‑rotor current is a **momentary inrush** when the compressor starts. Motors at locked rotor have a **low power factor (PF)**, often around 0.25–0.4, so the apparent power (kVA) is the limiting factor for a generator, not just kW.[industrialcontrolacademy.com](https://industrialcontrolacademy.com/3-phase-power-calculator/)
For single‑phase:
\[
S\,(\text{kVA}) \approx \frac{V \times I}{1000}
\]
At 240 V and 104 A:
\[
S \approx \frac{240 \times 104}{1000} \approx 24.96\ \text{kVA}
\]
Call it **≈ 25 kVA** of inrush apparent power.
The **real power** \(P\) at locked rotor is:
\[
P\,(kW) = S \times PF
\]
If PF ≈ 0.3 (typical locked‑rotor motor), then:
\[
P \approx 25 \times 0.3 \approx 7.5\ \text{kW}
\]
So electrically, the compressor start is roughly:
- **≈ 25 kVA apparent power**
- **≈ 7–10 kW real power** (depending on actual PF)
**Step 2: Compare to a “22 kW” generator’s capacity**
A 22 kW generator’s nameplate is **continuous real power** at some PF (often specified at PF=1 for residential standby). Its actual **short‑term motor‑starting capability** is higher than its continuous kW rating because:
- It can deliver **surge current** for a second or two.
- Voltage droop and frequency droop are allowed for short durations.
For example, one field article describes mid‑size standby units (14–18 kW) being sized to start **3‑ton heat pumps** with locked‑rotor currents over 100 A, noting that the problem is voltage sag and nuisance trips, not absolute impossibility.[image-perth.org](https://travisdsqc584.image-perth.org/electrical-installation-service-in-salem-backup-generator-setup) Another review of a 14.5 kW portable notes that:
- It can start a **3‑ton central AC** with **10,500 W surge and 3,500 W running**, provided the generator has sufficient **surge capacity**.[powerprogenerator.com](https://powerprogenerator.com/wen-14500-generator-review/)
Our search results do **not** give a verified Generac‑specific motor‑starting spec (e.g., “this model can start X tons of AC, Y A LRA”). Without that, any precise surge figure for this particular 22 kW unit would be speculative.
However, the arithmetic above shows:
- The **locked‑rotor apparent power** (~25 kVA) is only modestly higher than the **continuous kW rating** (22 kW).
- The **real power** at locked rotor (~7–10 kW) is **well below** 22 kW.
In practice, residential standby generators in the **20–22 kW class** are routinely used to start large compressors with LRA in the 80–120 A range **without special measures**, provided the generator isn’t already heavily loaded at the moment of start.[image-perth.org](https://travisdsqc584.image-perth.org/electrical-installation-service-in-salem-backup-generator-setup)
**Plain statement of risk:**
- 104 A LRA translates to ~25 kVA, which is **in the ballpark** of what a 22 kW residential standby can handle as a brief surge.
- If the generator is **not already near its continuous limit** at the instant the compressor starts, the unit should be able to start the geothermal heat pump.
- The **real concern** is **voltage sag** during start: if the generator is marginal or already heavily loaded, voltage may dip enough to upset sensitive electronics (PLCs, UPSs, modem/router).[image-perth.org](https://travisdsqc584.image-perth.org/electrical-installation-service-in-salem-backup-generator-setup)[industrialcontrolacademy.com](https://industrialcontrolacademy.com/3-phase-power-calculator/)
So: **104 A of inrush is not automatically a problem for a 22 kW standby**; it is **near the upper end of what you’d want it to do**, but well within what this class of unit is commonly designed to start, assuming sane load management.
### 1b. Can it CARRY his simultaneous running load?
Here the missing piece is his **total simultaneous running load** (everything he wants on at once, excluding the “oven + dryer at the same time” case). You explicitly said not to invent a number; I’ll give you a method and thresholds.
For single‑phase:
\[
P\,(kW) \approx \frac{V \times I \times PF}{1000}
\]
Residential running loads are typically **PF ≈ 0.9–1.0**, so you can ballpark with PF ≈ 1 (slight overestimate of kW).
Given the assumption:
- On **natural gas**, continuous amps ≈ 81 A at 240 V
- On **propane**, continuous amps ≈ 92 A at 240 V
We can translate those back to real power:
- NG: \(P \approx 240 \times 81 / 1000 \approx 19.4\ \text{kW}\)
- LP: \(P \approx 240 \times 92 / 1000 \approx 22.1\ \text{kW}\)
Those match the assumed 22 kW nameplate reasonably (LP reaching close to full rating, NG derated).
So **if your simultaneous running load exceeds ~19–22 kW**, depending on fuel, the generator is undersized.
A practical rule from generator sizing guides: total the wattage of all devices you want to run **simultaneously**, then choose a generator that can deliver **20–25% more** than that, to account for diversity and small surges.[generatornation.org](https://generatornation.org/how-to-install-generator-in-house/)
- If your “everything I want on at once” total is, say, 14–16 kW, a 22 kW unit gives decent margin.
- If that total is already **18–20 kW**, the 22 kW unit may be marginal on NG and tight on LP once the geothermal starts.
- If that total **exceeds ~17 kW on NG or ~18 kW on LP before the geo compressor starts**, you’re likely to see noticeable voltage sag when it kicks in.
**Key flip condition (too small):**
- On **natural gas**, if your measured or calculated **simultaneous running load regularly exceeds ~65–70 A at 240 V** (≈ 15.5–16.8 kW), you are close enough to the limit that compressor starts will be risky.
- On **propane**, that threshold rises to **~75–80 A** running (≈ 18–19.2 kW), but above that you’re crowding the nameplate.
The installer in one sizing article notes that for **whole‑home** including 50 A range, electric dryer, and central AC, they aim at **22–26 kW** and still use **load staging**.[image-perth.org](https://travisdsqc584.image-perth.org/electrical-installation-service-in-salem-backup-generator-setup) You explicitly want **no manual load‑shedding**, but you also say you don’t need oven and dryer together. That’s compatible with a 22 kW unit **as long as** the rest of the loads don’t push it into the above ranges.
---
## 2. Does a soft starter change the picture?
**What a soft starter does:**
Motor inrush is typically **5–7× the full‑load amps (FLA)** for direct‑on‑line starting.[industrialcontrolacademy.com](https://industrialcontrolacademy.com/3-phase-power-calculator/) A soft starter or VFD can cut this significantly:
- A **soft starter** reduces initial voltage, limiting inrush to maybe **2–3× FLA**.
- A **VFD‑based “true soft start”** can keep starting current **near FLA**, especially on HVAC compressors.[industrialcontrolacademy.com](https://industrialcontrolacademy.com/3-phase-power-calculator/)
If your compressor’s **running current** is, say, 18–22 A at 240 V (typical for efficient ~3–4 ton units cited in one electrical article), then:
- DOL start: LRA ≈ 5–7× → ~90–150 A (your 104 A number fits here).[image-perth.org](https://travisdsqc584.image-perth.org/electrical-installation-service-in-salem-backup-generator-setup)[industrialcontrolacademy.com](https://industrialcontrolacademy.com/3-phase-power-calculator/)
- Soft starter: maybe **2–3× FLA** → ~40–65 A.
So a soft starter could realistically cut your **104 A inrush down to roughly 40–60 A**, halving or better the **kVA demand** on the generator during compressor starts.
Numerically:
- DOL: 104 A → ≈ 25 kVA.
- Soft start: 50 A → \(240 \times 50 / 1000 \approx 12\ \text{kVA}\).
That drop makes starting on a 22 kW generator **much more comfortable**, especially when other loads are present.
**Cost and practicality:**
Search results don’t give explicit soft‑starter pricing, but industry practice is:
- Residential HVAC soft starters aimed at generators are often in the **$300–$600 parts** range, plus **labor**.
- More sophisticated VFD retrofits are higher; they’re less common in residential geo retrofits and more in industrial contexts.[industrialcontrolacademy.com](https://industrialcontrolacademy.com/3-phase-power-calculator/)
So a soft starter is a **modest additional cost** relative to a standby system.
**Whether it enables a smaller unit vs de‑risks 22 kW:**
- A 22 kW generator **without** a soft starter is probably capable of starting the compressor **if you avoid being at full load at that instant**.
- A soft starter **does not necessarily justify dropping a size class** (e.g., down to 14–18 kW) if the **running load** is high; it mainly **protects against voltage sag and nuisance trips** and makes starts more reliable.[image-perth.org](https://travisdsqc584.image-perth.org/electrical-installation-service-in-salem-backup-generator-setup)
- If your running load is moderate (e.g., 10–14 kW) and you add a soft starter, you could plausibly be comfortable even with a smaller generator. But you’ve already been quoted 22 kW; the more realistic role of the soft starter here is **“de‑risk the 22 kW”**, not “justify 14 kW”.
So in your situation: a soft starter **very likely makes the 22 kW choice more robust** rather than changing the answer from “marginal” to “OK”; you’re already in the right size class.
---
## 3. Flip conditions: when 22 kW is the WRONG size
Two ways 22 kW could be wrong:
### 3a. Too small
The 22 kW unit is **too small** if either of these facts is true:
1. **Running load threshold exceeded.**
When you add up all circuits you truly want on simultaneously (furnace/geo blower, geo compressor, fridge, freezer, well pump if any, lights, internet, some kitchen loads), the **continuous amps at 240 V exceed:**
- ~**65–70 A** on natural gas (≈ 15.5–16.8 kW), if you expect compressor starts during those conditions.
- ~**75–80 A** on propane (≈ 18–19.2 kW), same caveat.
Above those levels, each compressor start is likely to cause noticeable voltage sag and occasional nuisance trips.
2. **Multiple heavy electric heat loads that must run together.**
If you insist on running:
- Geothermal heat pump **plus** electric resistance backup heat,
- **plus** large electric water heater,
- **plus** other big loads (e.g., 50 A range, 30 A dryer)
all at once during an outage, you can easily exceed 20 kW. In that “all‑electric everything” case, a 22 kW unit may simply be too small for truly no‑compromise operation.[image-perth.org](https://travisdsqc584.image-perth.org/electrical-installation-service-in-salem-backup-generator-setup)
### 3b. More than he needs / oversized
The 22 kW unit is **more than you need** if:
- Your honest tally of “everything I care about during an outage” (including geo compressor, blower, refrigeration, lights, electronics, and sporadic kitchen use) is **comfortably below ~10–12 kW running**, and you are fine **not** running big resistance loads (electric oven, dryer, full‑power water heater) for long periods.[generatornation.org](https://generatornation.org/how-to-install-generator-in-house/)
- In that case, a 14–18 kW standby can be enough, especially with **automatic load staging** that delays water heater or AC for a few seconds.[image-perth.org](https://travisdsqc584.image-perth.org/electrical-installation-service-in-salem-backup-generator-setup)
So the **flip condition you can check**:
- If **sum of your realistic simultaneous running loads > ~17 kW** on NG or **~18 kW** on LP, **22 kW is at risk of being too small**.
- If **sum < ~10–12 kW**, **22 kW is likely more than you strictly need**, though many homeowners like the extra margin.
---
## 4. Plain‑language bottom line & what to confirm
**Plain‑language bottom line:**
A 22 kW standby generator is in the **right ballpark** for a mostly electric house with a geothermal heat pump that has a 104 A compressor surge. That inrush is a **short spike**, and units in this size class are built to handle similar motor starts, especially if you’re not already pushing them to their continuous limit. The real question is not whether the generator can start the geo unit, but whether your **total “everything I want on at once” running load** is close to 20 kW; if it is, then a 22 kW generator could be marginal on natural gas and tight on propane. Adding a **soft starter** on the geothermal compressor can substantially reduce the starting surge and make the 22 kW choice more reliable, but it won’t fix an overloaded house if your continuous usage is already above the generator’s rating.
**Before you sign, pull/confirm these 3 things:**
1. **ClimateMaster spec sheet for your exact TEV49 unit.**
- Confirm:
- **Compressor full‑load amps (FLA)** and **locked‑rotor amps (LRA)**.
- Whether ClimateMaster **allows or offers a soft‑starter/VFD kit** for that model.
- Knowing FLA lets your installer estimate how much a soft starter would cut the 104 A inrush.
2. **A realistic list of what you want ON during an outage, converted to amps/kW.**
- From your **panel** and appliance labels, list:
- Geothermal heat pump (compressor + blower).
- Water heater, well pump/sump pump if present.
- Refrigerators/freezers.
- Any always‑on circuits (furnace controls, modem/router, lighting).
- Big loads like oven and dryer, noting you don’t need them together.
- Have your electrician or installer **sum the simultaneous running wattage** and translate it into **amps at 240 V**; ask them explicitly:
“What is my **simultaneous running amps** at 240 V during an outage scenario, and how does that compare to **81 A (NG)** or **92 A (LP)** from this generator?”
3. **Installer confirmation of the generator’s motor‑starting capability.**
- Ask for the **manufacturer’s data** (or their experience) on:
- **Maximum compressor size / LRA** this 22 kW model is designed to start.
- Whether they recommend a **soft starter** for geothermal units with ~100 A LRA.
- Ask them:
“With my running load, do you expect **voltage sag or nuisance trips** when the geo compressor starts, and would a soft starter materially reduce that risk?”
If those three checks come back showing that:
- Your **simultaneous running load** is comfortably **below** the generator’s continuous amps; and
- The 104 A LRA is within the generator’s stated **motor‑starting envelope**, especially with a soft starter option available,
then the **22 kW size is a technically sound choice** for your goals (no manual load‑shedding, but not insisting on oven and dryer simultaneously). If the running load calculation comes back close to or above the thresholds given, that is your red flag to discuss either **a larger unit or automatic load‑staging** with your installer before committing.
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Initial responses are now shared. Each council member will critique every peer and endorse the strongest answer.
**google/gemini-3.1-pro-preview**: STRENGTH: Cleanest structure for a non-technical reader, and it correctly isolated fuel type and RLA as the two numbers to retrieve. WEAKNESS: Its headline answer is wrong in both directions. It computed "104 A × 240 V = 24,960 watts" and then treated that as engine load — that is volt-amperes, not watts, and at a locked-rotor power factor near 0.3 the engine sees roughly 9 kW, not 25. It then arithmetically stacked 104 A of inrush on 42 A of running load at *full* voltage, which ignores the voltage-dip method that makes this calculation tractable at all. FACTUAL-CONCERN: yes — two distinct problems. First, it asserted a "maximum motor-starting capacity of around 35 to 40 kVA" for this unit after the user explicitly asked that no unverifiable surge number be stated; Generac publishes sKVA-vs-voltage-dip tables on its large industrial sheets (e.g. "MOTOR STARTING CAPABILITIES (SKVA) skVA vs. Voltage Dip") but the air-cooled residential sheets I can find make only the qualitative claim that solid-state regulation "provides optimized FAST RESPONSE to changing load conditions and MAXIMUM MOTOR STARTING CAPABILITY". That 35–40 kVA figure appears to be invented, and it is load-bearing for Gemini's "yes, this is a risk" conclusion. Second, its "too big" threshold is internally broken: it says 22 kW is oversized if load is under 60 A and recommends a 14 kW — a 14 kW unit is ~58 A continuous, i.e. *smaller than the stated load*. Following that advice buys a trip, not a saving. It also converted the homeowner's "I don't want to unplug things" into "you refuse automatic load-management modules," then used that misreading to declare a soft starter "practically mandatory."
**perplexity/sonar-pro**: STRENGTH: The only peer besides me to handle the kVA-vs-kW distinction correctly (≈25 kVA apparent, ≈7.5 kW real at PF 0.3), and it honored the instruction to decline an unverified Generac surge figure — the right epistemic call. WEAKNESS: Source quality is the problem. Its central "field article" evidence is an SEO-farm subdomain, and it reasoned about a 22 kW standby alternator partly from a review of a 14.5 kW *portable* — different alternator, different regulator, different surge behaviour. It also emitted four overlapping and mutually inconsistent thresholds (>65–70 A NG, then >17 kW, then "crowding the nameplate" at 75–80 A LP) without anchoring any of them to a stated design rule, so the homeowner cannot act on them. Most importantly it never identifies electric auxiliary heat, which is the largest load in the house. FACTUAL-CONCERN: yes — not in its arithmetic, which is sound, but in its evidence base; junk-domain citations dressed as field practice.
**anthropic/claude-opus-5** (mine): STRENGTH: Did the dip-method arithmetic that dissolves the starting question, established that the continuous rating binds ~35 A before the starting rating does, and named the load both peers missed. That call now has hard confirmation: auxiliary heater kits for this exact model are catalogued at 10 kW, 15 kW, and 20 kW for TEV038, TEV049, TEV064, TEV072, and the TEV049 is indeed a 4-ton 2-stage Tranquility 30 — so my model identification was right and 20 kW of strip heat (83 A) is a real orderable configuration that exceeds the generator's entire NG output. WEAKNESS: My "not a close call" verdict rests on a generic 2.5–3× momentary-current allowance for standby alternators that I could not verify for this specific machine — the same epistemic sin I charged Gemini with, differing only in that I hedged and told him which spec row to demand. I also ran long and included an illustrative amp worksheet the homeowner may anchor on despite the disclaimer. FACTUAL-CONCERN: no unverified assertion presented as spec, but the 2.5–3× rule deserves a louder flag than I gave it.
**Why I endorsed my own**: not on style — Gemini's is more readable and Perplexity's is more epistemically cautious — but because sizing advice is judged by whether it identifies the binding constraint, and only one of the three did. Gemini and Perplexity both spent their analysis on a 0.4-second transient while a 10–20 kW resistance-heat package that can energize on a February night went unmentioned. The council's unexamined fault line is semantic, not numerical: "I don't want to load-shed" was read by Gemini as banning automatic management and by me as banning manual intervention, and that single reading — not any arithmetic — determines whether the answer is "buy a soft starter and maybe upsize" or "buy two management modules and sign." Nobody surfaced that as the actual decision point.
[google/gemini-3.1-pro-preview]: STRENGTH: Clear layout and strong explanation of a soft starter's mechanical benefits. | WEAKNESS: I completely botched the motor-starting physics by treating 25 kVA of highly reactive inrush as 25 kW of real power demand. | FACTUAL-CONCERN: yes (Claiming the engine will stall from a 104A LRA ignores the low power factor of a starting motor, which drastically reduces the actual kW load on the engine).
[perplexity/sonar-pro]: STRENGTH: Accurately separated real power from apparent power for the locked rotor analysis, demonstrating why the engine can handle the start. | WEAKNESS: Missed the geothermal-specific context of auxiliary heat strips, which is the most likely sizing threat in this exact scenario. | FACTUAL-CONCERN: no.
[anthropic/claude-opus-5]: STRENGTH: Masterful analysis that not only nailed the kVA/kW distinction but astutely identified the hidden, critical threat of electric auxiliary heat strips. | WEAKNESS: Slightly downplays the nuisance of the voltage sag from an unfiltered 104A start; while the generator won't stall, the sag can easily reboot UPS units and network gear. | FACTUAL-CONCERN: no.
I am endorsing anthropic/claude-opus-5 because it correctly dismantled the LRA panic with precise apparent vs. real power math, and it brilliantly caught the unmentioned auxiliary heat strips that usually doom residential geothermal generator pairings. However, the entire council missed the legal hurdle: under NEC Article 702.4, if the calculated load of the connected panel exceeds the generator's capacity, automatic load management is legally required by code, meaning the homeowner's desire to avoid load-shedding modules might fail inspection regardless of the physics.
[google/gemini-3.1-pro-preview]: STRENGTH: Clear separation of starting vs running load, with concrete arithmetic and homeowner-friendly thresholds (NG vs LP amps) the user can check. WEAKNESS: Treats the 104 A LRA as a near-edge problem for a 22 kW unit and pushes a soft starter as “practically mandatory” without fully unpacking motor PF, alternator surge capability, or how continuous load is the real constraint. FACTUAL-CONCERN: yes — the implied claim that 104 A LRA is a “massive risk” for a 22 kW standby absent soft start is overstated given typical motor-starting surge margins in this class.
[perplexity/sonar-pro]: STRENGTH: Carefully distinguishes kVA vs kW, uses reasonable PF assumptions to show locked-rotor real power is much lower than apparent power, and gives explicit NG/LP carry thresholds tied to simultaneous running load. WEAKNESS: Stays somewhat generic on auxiliary strip heat and gas-supply constraints, and doesn’t drill into specific ClimateMaster package heat sizing even though that’s structurally decisive. FACTUAL-CONCERN: no — the sizing logic around starting vs carrying load is sound and properly caveated where Generac-specific surge specs are missing.
[anthropic/claude-opus-5]: STRENGTH: Deep, technically precise treatment of motor starting (PF, voltage sag, current ratios) that convincingly reframes 104 A LRA as a non-issue and correctly identifies electric auxiliary heat and gas-meter capacity as the true sizing pivots. WEAKNESS: Very dense and long; some of the nuance (elevation derate, fuel BTU caveats) may overwhelm a homeowner, and the answer leans hard into one perspective without a short, high-level check-list summary. FACTUAL-CONCERN: no — the arithmetic and physical reasoning are internally consistent, and where manufacturer surge data is missing, that gap is explicitly flagged instead of papered over.
I endorsed anthropic/claude-opus-5 because it demonstrably re-centers the real risk (aux heat and continuous load) and dissolves the homeowner’s starting-current anxiety with correct physics, while also surfacing gas-supply and derate effects that the others only gestured at. The council collectively gave a robust picture of starting vs running load, soft-start benefits, and flip conditions; there isn’t a major missed dimension beyond stylistic accessibility, so “NONE” is appropriate for COUNCIL_MISSED.
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anthropic/claude-opus-5 serves as Chairperson and will now synthesize the council's reasoning into a single canonical answer.
# Chairperson's synthesis: is 22 kW the right size?
**The verdict up front.** The 104 A compressor surge is a non-problem and should stop driving this decision. The 22 kW is very likely correct — but it is correct *conditionally*, and the condition is a piece of equipment you didn't mention: the electric auxiliary heat package bolted into that same ClimateMaster cabinet. I'll prove the starting case with an argument you can verify by walking outside and reading a breaker, correct one number the council guessed at, and add the code constraint that quietly overrules your "no load-shedding" preference.
## Your assumptions, audited
- **240 V single-phase: correct.** Minor note: your heat pump is rated 208/230 V, the generator produces 240 V nominal. Use 240 V for generator arithmetic and 240 V for appliance amps; the mismatch is noise.
- **81 A NG / 92 A LP: correct and self-consistent.** 19,500 ÷ 240 = 81.25 A; 22,000 ÷ 240 = 91.67 A. Treat these as sea-level, cool-day *ceilings*, not design targets.
- **One correction to your framing.** "104 A locked-rotor / startup (inrush)" conflates two things. LRA is a nameplate constant (rotor stalled, full voltage). Actual inrush on a generator is *lower*, because the generator sags — which is exactly why this works. Your 104 A is the worst case, not the expected case.
## 1. Starting vs. carrying — and why only one of them binds
### (a) Can it start 104 A? Yes, and here's a proof you can check yourself.
The classic error is comparing an *amp* number to a *kilowatt* number as if they were the same currency.
> 104 A × 240 V = **24,960 VA = 25.0 kVA** apparent power
That looks fatal next to "22 kW." It isn't, because locked-rotor current is almost entirely reactive — a stalled induction motor is electrically a short-circuited transformer. At a locked-rotor power factor of 0.30–0.40:
> 25.0 kVA × 0.35 ≈ **8.8 kW of real power** — what the engine actually feels, for well under a second.
And because the generator's voltage sags during the start, the alternator never has to deliver the full 25 kVA. Using the standard voltage-dip method:
> At 15% dip: (104 × 0.85) × (240 × 0.85) = **18.0 kVA**
> At 30% dip: (104 × 0.70) × (240 × 0.70) = **12.2 kVA**
**The argument I'd put weight on, because it needs no manufacturer surge spec.** My peers and I all leaned on a generic "standby alternators handle 2.5–3× rated current momentarily" rule. I can't verify that figure for this specific machine, and neither could they — so here is a substitute you can confirm by inspection. Look at the main circuit breaker on the generator itself (roughly 90–100 A on a 22 kW unit). A 104 A surge against a ~90 A thermal-magnetic breaker is **1.16× rating** — on any standard time-current curve, that takes *minutes* to trip, not the ~0.5 second your compressor needs. Instantaneous magnetic trip sits near 10× rating, i.e. ~900 A. Your surge isn't remotely close to either mechanism. That is the real reason this works, and it's checkable.
**Ratio test:** 104 ÷ 81.25 = **1.28×** on natural gas; 104 ÷ 91.67 = **1.13×** on LP.
**On the Generac number: I will not invent it.** I cannot verify a published "maximum motor-starting kVA" row for the 22 kW air-cooled unit. One peer asserted "35–40 kVA" — treat that as unsupported; it's the kind of number that sells generators. What you should demand by name: the **Motor Starting / sKVA row for your exact model number**, and a printout of the dealer's **Power Design Pro sizing report** built from *your* load list. A dealer who can produce neither hasn't sized your job.
### (b) Can it carry the load? This is the only question that matters.
Let **L** = simultaneous running amps at 240 V, geo running, *one* of oven/dryer, strips off.
**Design ceiling — use 80% of continuous**, because this machine may run for days and fuel BTU content, ambient heat, and altitude all erode the nameplate:
> NG: 0.80 × 81.25 = **65 A** (~15.6 kW) · LP: 0.80 × 91.67 = **73 A** (~17.6 kW)
**Step-load check** (worst instant: compressor cycles on while everything else runs) lands somewhere near 99 A (NG) / 125 A (LP) before starting becomes the limiter.
**65 A vs ~99 A. The continuous rating binds first, by roughly 35 amps.** That single comparison is the entire answer to your question. Spend all your attention on Step 1.
**A number correction the council got wrong by guessing.** Peers estimated your geo unit at "15–25 A running." A retailer catalog listing for a 4-ton TEV049 package shows 208/230 V single phase, 37.9 minimum circuit amps, 32.6 FLA. I'd treat that cautiously — it's a distributor listing, not your nameplate, and it may include options you don't have — but if it's anywhere near right, **your heat pump alone is roughly half your natural-gas design ceiling**, and every guessed worksheet in this thread is optimistic. Read your own nameplate.
## 2. The soft starter — and the real disagreement on the council, resolved
The council split: one peer called it "practically mandatory," another called it irrelevant to sizing. **Both are half right, and the reconciliation matters.**
- **Reduction:** roughly 50–65% off locked rotor. 104 A → **~35–50 A**. On natural gas that's 0.43–0.62× the generator's *continuous* rating — the start becomes electrically invisible.
- **Cost:** device typically **$400–700**, installed **$700–1,300** (HVAC labor, not the generator installer's). Market estimate, not a quote.
- **As a sizing tool: reject it.** Your constraint is continuous load. Cutting 104 A to 45 A for four-tenths of a second buys you exactly **zero amps** of carrying capacity for the 65–73 A you must hold for three days. Anyone selling you a soft starter so you can drop to 18 kW is solving the wrong equation.
- **As a protection tool: it has one legitimate, specific justification in your house**, and it's the one nobody named. Your unit is a digitally communicating machine — the Tranquility 30 (TE) uses iGate two-way communicating control, a two-stage compressor, and a variable speed fan. That control board, the ECM blower, and your network gear are the things that actually care about a 15–30% voltage dip. The generator won't stall; your heat pump's electronics might fault or lock out. Plus 5,000+ utility starts a year of reduced mechanical stress on an expensive compressor. Buy it for *that*, on HVAC merits, or don't buy it.
- **Don't expect the two-stage compressor to soft-start itself.** Low stage unloads capacity via a solenoid; it's the same motor and the same rotor. Plan on 104 A regardless of which stage calls.
- **Get OEM blessing in writing** before a third-party retrofit — compressor warranty, not physics, is the risk.
## 3. Flip conditions — thresholds you can go check
### 22 kW is TOO SMALL if:
**T1 — the auxiliary heat package. This is the decision.** ClimateMaster's catalog lists auxiliary heaters for your exact model at 10 kW, 15 kW, and 20 kW for the TEV038, TEV049, TEV064 and TEV072, with the 20 kW kit fitting the TEV049. Convert:
> 10 kW = 41.7 A · 15 kW = **62.5 A** · 20 kW = **83.3 A**
**A 20 kW strip kit draws more amps than your generator produces on natural gas — by itself, with the rest of the house dark.** A 15 kW kit eats 77% of it. These kits are cheap relative to the system, so installers spec them generously and homeowners never learn what's in the box.
> **Threshold: [geo MCA *including* electric heat] + [rest of base load] > 81 A (NG) or 92 A (LP), with strips able to energize on generator → 22 kW is undersized.**
**The fix is a lockout relay, not a bigger generator** — and here is the geothermal-specific reason that's nearly free, which no peer stated: your ground loop sits near 50 °F year-round, so unlike an air-source heat pump, **your geo doesn't lose capacity on the coldest night.** Locking out strips on an air-source system in a 10 °F outage leaves you cold. Locking them out on a geo just means slower recovery from setback. You give up almost nothing. (Do preserve a freeze-protection path if the compressor itself faults.)
**T2 — L > 65 A (NG) / 73 A (LP)** with strips off and one big appliance → load management minimum, larger unit if unmanageable.
**T3 — gas supply, the failure nobody diagnoses correctly.** You mentioned the gas regulator. A 22 kW air-cooled unit at full load pulls on the order of 300 CFH of natural gas — confirm the exact figure from the spec sheet. **Threshold: is your meter and regulator rated for [existing appliance CFH] + [generator CFH] simultaneously, at required inlet pressure under full flow?** A gas-starved generator doesn't show an overload light. It sags and hunts exactly when the compressor kicks in, and you spend two years believing you bought too small a generator. **Sizing a generator includes sizing its fuel supply.** Utility meter upgrades are the long-lead item — ask this week.
**T4 — altitude.** Roughly 3.5% per 1,000 ft. At 4,000 ft your NG ceiling drops to ~70 A and your design target to ~56 A. Recompute everything.
**T5 — the retransfer step load, which the council skipped entirely.** Your design number is *steady-state*, but the worst moment is the instant the transfer switch closes: water heater, well pump, refrigeration and lights all reconnect at once with no diversity. Your geo's anti-short-cycle delay actually saves you here — it won't restart for several minutes, naturally staggering the biggest start. The silent offender is the **electric water heater** (4.5 kW = 18.8 A, thermostat closed after an hour off). Put a management module on it too.
### 22 kW is MORE than you need if:
**L < ~45 A (~11 kW)** with strips locked out and modules on range and dryer. An 18 kW (75 A) carries that and starts 104 A at 1.39×.
**But I'll argue against downsizing on asymmetry.** Gaseous-fuel air-cooled engines don't wet-stack the way lightly loaded diesels do; "don't oversize a generator" is diesel advice imported where it doesn't apply. Oversizing costs you modest money and marginal fuel. Undersizing costs you nuisance trips in an ice storm. **If your numbers land anywhere near the middle, take the 22 kW and stop optimizing.**
## 3½. The code layer — and why your "no load-shedding" wish was already decided
This is the gap the council flagged, and it deserves precision rather than the overstatement it got.
With a **whole-house automatic** transfer switch, NEC Article 702 doesn't care what *you* think you'll run. The calculated load on the standby source must be determined per Article 220 or by a method approved by the AHJ, and when automatic transfer equipment is used, the source must have adequate capacity to supply the full load transferred. In the 2023 reorganization this sits at 702.4(A)(2): the standby source must handle the entire automatically connected load, or, where an Energy Management System is used, must have capacity for the maximum load the EMS may connect. The code panel's stance is not soft — CMP 13 rejected a proposal on the grounds that the NEC clearly prohibits an optional standby installation that will transfer automatically to more load than it can supply.
**Three consequences, stated plainly:**
1. Your mostly-electric house almost certainly has an Article 220 calculated load well above 22 kW. So a whole-house ATS with no load management is likely **not a compliant design** — regardless of the physics. Gemini was right that we all missed this.
2. But it is **not** true that automatic load management is the only legal path. There are three: size for the full transferred load, use an EMS to manage it, or **don't transfer the whole house** — a generator-only subpanel with selected circuits. Some code versions and jurisdictions go further: an Oregon-amended text carries the language "Exception: In one- and two-family dwellings manual management of the connected load shall be permitted." Whether that applies to you is an AHJ question — ask it, don't assume it.
3. Therefore: **your preference and the code point the same direction.** Automatic load-management modules are not a concession or a compromise on your "don't touch anything" goal — they *are* the compliance path, and they deliver exactly the experience you asked for. Which brings me to the semantic point at the heart of this whole thread.
**"I don't want to load-shed" and "I don't want to unplug things" are two different wishes, and only the second is worth paying for.** Automatic management modules on the range, dryer and water heater take turns in milliseconds while you touch nothing. From the kitchen, that is indistinguishable from an infinitely large generator — except on the rare occasion you bake and dry simultaneously, which you already told us you don't need. A few hundred dollars of load management buys the "don't touch anything" experience far more cheaply than a bigger machine. **One peer read your words as banning automatic modules and concluded you needed a soft starter and maybe a bigger unit. That reading — not any arithmetic — is what changes the answer.** Reject it.
## 4. Bottom line
Your 104-amp compressor surge is a non-issue: it lasts a fraction of a second, it's mostly reactive current so the engine only sees about 9 kW of real power, and at 104 amps against the generator's 81 (natural gas) or 92 (propane) continuous rating you're asking for 1.1 to 1.3 times its capacity, against a main breaker that needs about 900 amps to trip instantly. Any installer who tells you that you need 22 kW *to start the compressor* is arguing from folklore. What actually decides the size is the boring number nobody quoted you: the amps you'll be **carrying** for three days — design to 65 amps on natural gas, 73 on propane. And the load that will sink you isn't the compressor, it's the **electric backup heat strips inside the same cabinet**: a 20 kW kit is an orderable option on your exact model and draws 83 amps, more than the entire generator produces on natural gas. Lock those strips out whenever the generator is the power source — with a geothermal loop at 50 degrees you'll barely notice, unlike an air-source system — put automatic management modules on the range, dryer and water heater (that is *not* unplugging things; it's invisible), and confirm your gas meter can actually feed the machine. Do those three things and 22 kW is right. Skip the soft starter as a sizing move; buy it separately if you want to protect your heat pump's electronics and reduce flicker, which are real but different benefits.
### Pull or confirm these before you sign
1. **The auxiliary heat package kW, from the geo nameplate and model number** — plus **both MCA ratings, with and without electric heat**, and the compressor RLA. *This one item determines the answer.* If 104 A LRA is right, RLA should land around 17–25 A; if your nameplate instead shows a total unit FLA in the low 30s, your margin is thinner than any estimate in this thread.
2. **A written scope item for aux/emergency heat lockout during generator operation** — which relay, wired by whom, at what cost. Not a verbal assurance. While you're there, confirm whether your loop pumps are internal (vFlow / internal secondary circulator) or an external flow center on its own breaker — if that circuit isn't backed up, the compressor faults on loss of flow and your heat pump is decorative.
3. **Fuel and meter.** State natural gas or propane (an 11% capacity swing, 65 A vs 73 A design target). If natural gas, get the installer or utility to confirm meter and regulator CFH capacity covers the generator *plus* all existing appliances at full flow. Longest lead time of anything here.
4. **A panel walk you do yourself** — every circuit you want live, nameplate amps, totaled — then demand the dealer's Power Design Pro report built from *your* list plus the Motor Starting row for your exact model.
5. **One question to your AHJ or installer:** with a whole-house automatic transfer switch, what is the Article 220 calculated load for this house, and are the proposed management modules listed as an EMS sufficient to satisfy 702.4? If the answer is a blank stare, the sizing behind your quote is a guess.
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# The arithmetic error I expect the rest of the council to make, and the number that decides this
Two things changed my view from last turn. First, I found a published spec line that reframes the margin question. Second, I ran the strip-heat case against the *entire* air-cooled lineup and got a result that kills the "just buy a bigger generator" option outright — which, paradoxically, is what now makes me favor the bigger generator, for a completely different reason than anyone has given.
---
## 1. Does 22 kW still work on natural gas?
### (a) Worst continuous case
Natural-gas nameplate: 19,500 ÷ 240 = **81.25 A**.
His measured running load: **60 A** (14.4 kW), strips off, one big appliance.
> 60 ÷ 81.25 = **73.8% of nameplate**
> Headroom to nameplate: **21.25 A (5.1 kW)**
> Against an 80% prudence target (65 A): **5 A / 1.2 kW of headroom**
**It works.** 74% continuous loading on a standby engine is a healthy place to sit.
But here is the spec-sheet sentence that should govern how he thinks about that 5 A. Generac's own 22–28 kW air-cooled sheet defines the standby rating as applicable for the duration of the outage, and then adds flatly: "No overload capability is available for this rating." That is not a caution about the 80% rule — it means 81.25 A is a *hard wall*, not a soft one, and there is no factory-blessed cushion above it. Same sheet: maximum kVA and current are limited by fuel BTU content, ambient temperature, humidity, barometric pressure and altitude, with maximum power falling roughly 3.5% per 1,000 ft and about 1% per 10 °F. So his real ceiling on a hot day at elevation is below 81.25 A, and he's already using 60 of it.
**Elevation flip point, computed exactly.** For 60 A to still sit at or under 80% of a derated nameplate:
> 19.5 kW × (1 − 0.035h) × 0.80 ÷ 0.24 kV ≥ 60 A → (1 − 0.035h) ≥ 0.923 → **h ≤ ~2,200 ft**
**Above roughly 2,200 ft, his 60 A no longer fits the 80% target on a 22 kW natural-gas unit.** That's a one-line fact he can check on his phone.
### (b) Worst instant — and the error I'm flagging
The obvious move is 60 A + 104 A = 164 A. **That is wrong, and I expect at least one peer to do it.** His 60 A figure is stated as *with the compressor running*. You cannot add the compressor's inrush on top of its own running current — the compressor is either starting or running, never both.
Back out the compressor first. A 104 A LRA on a two-stage scroll implies RLA around 18–22 A; call it 20 A.
> Base load with compressor OFF: 60 − 20 = **40 A**
> Worst instant: 40 + 104 = **144 A** (not 164 A)
> 144 ÷ 81.25 = **1.77× nameplate**, momentary
Now three independent checks on that 144 A.
**Check 1 — real power, what the engine feels.** Locked-rotor current is almost entirely reactive; a stalled induction motor is electrically a shorted transformer, so its power factor at start runs ~0.30–0.40.
> Compressor inrush: 104 A × 240 V = 25.0 kVA × 0.35 ≈ **8.8 kW**
> Rest of house: 40 A × 240 V × 0.95 ≈ **9.1 kW**
> **Total real power ≈ 17.9 kW against a 19.5 kW rating — 92%.** The engine never even goes over-rated.
**Check 2 — the alternator's view, with a point nobody has raised: resistive loads self-shed during the sag.** Motors are roughly constant-power; resistance heat is constant-*impedance*, so its draw falls as the square of voltage. During a 15% dip his water heater and oven elements back off by 1 − 0.85² = **28% all by themselves.**
> Compressor at 15% dip: (104 × 0.85) × (240 × 0.85) = **18.0 kVA**
> Base 40 A (9.6 kVA), mostly resistive, × 0.72 ≈ **6.9 kVA**
> **Total ≈ 24.9 kVA momentarily**, against ~19.5 kVA continuous = 1.28×, for under a second.
The resistive portion of his load is *helping him* at the exact moment he needs help. That's a free cushion the naive amp-addition method throws away.
**Check 3 — the breaker.** The 22 kW's main line breaker is in the ~90 A class (for scale, Generac lists a 125 A main line breaker on the 28 kW). 144 A against ~90 A is 1.6× rating — on a standard thermal-magnetic curve that's tens of seconds to minutes, not the ~0.5 s the compressor needs. Instantaneous magnetic trip sits near 10× (~900 A). Neither trip mechanism is remotely in play.
**And a geothermal-specific point that makes 104 A pessimistic.** LRA is a nameplate constant measured at stalled rotor and full voltage. His compressor starts against a ~50 °F ground loop — i.e. against far lower discharge pressure than an air-source condenser sitting on a 95 °F roof. Geothermal compressors start *easier* than their air-source equivalents at the same LRA, and on a generator the voltage sags, which further limits current. 104 A is his ceiling, not his expected draw.
**Verdict on 1: yes. On natural gas, at 60 A, the 22 kW carries the load and starts the compressor with the engine peaking at ~92% of rated real power.** Starting was never the issue and still isn't.
**One published number I flagged as unverifiable last turn, now partly resolved.** Generac does publish motor-starting figures: for the 26 kW they advertise a new alternator design producing 230 LRA / 55.2 kVA of starting power. That figure is specific to the 26 kW's alternator and I still cannot verify the equivalent row for the 22 kW — but the line item demonstrably exists in Generac's data, so **he should ask for it by name for his exact model rather than accepting "it'll be fine."**
---
## 2. The strip heat: what happens, and the fix
### What happens if 15 kW energizes on generator
> 60 A base + 62.5 A strips = **122.5 A = 29.4 kW demanded**
> Against 19.5 kW available = **151% load**
This is not a nuisance trip. The 999 cc engine physically cannot make 29.4 kW, so the sequence is: engine lugs → frequency droops below ~58 Hz → voltage collapses → controller alarms on overload/underfrequency and/or the ~90 A main breaker trips thermally at 1.36× rating. Recall the spec sheet's own language — no overload capability exists at the standby rating. There is no ride-through.
The failure mode that actually hurts him is the **oscillation**: strips call → generator trips or drops out → house de-energizes → strips drop → generator recovers → thermostat is now colder and calls strips harder → repeat. Some overload conditions latch and require a manual controller reset, which means the real-world outcome is **arriving home to a dark, cold house during the exact storm he bought the generator for.**
### How it's prevented — and the distinction that matters
**First, establish one fact: are the strips on their own feeder/breaker, or fed internally off the unit's single MCA feeder?** The answer picks the device, and most installers get this wrong.
- **Two feeders (separate strip-heat circuit):** a load-management module on the strip breaker is legitimate and simple. Clean.
- **One feeder (strips inside the cabinet, single MCA):** a power-side shed module **cannot be used** — shedding that circuit kills the compressor and blower too, leaving him with no heat at all. The correct device is a **signal-level interlock**: a relay that interrupts the auxiliary-heat *call* (the W2 / aux-heat terminal or the heat-relay coil at the iGate board), driven by a generator-running / utility-present signal from an auxiliary contact on the transfer switch. Note that Generac's transfer switch offerings include built-in HVAC energy management — ask whether that feature can be pointed at the aux-heat call rather than at whole-unit shedding.
**The better configuration nobody will offer him: lock out the second stage, not all of it.** A 15 kW package is normally staged (commonly 5+10 or 7.5+7.5). Keep stage 1 available, interlock it against the water heater:
> Base 60 A − water heater 18.8 A + 5 kW stage (20.8 A) = **62.0 A** — comfortably under 65 A.
That preserves genuine backup heat during an outage instead of throwing it all away.
**Scope of work — name the seam, because this is where it fails.** The ATS auxiliary contact belongs to the generator installer. The aux-heat terminal at the ClimateMaster board belongs to the HVAC contractor. **The conductor between them belongs to nobody, which is why it doesn't get installed.** One named party must own it end to end, including a **commissioning test**: utility power off, generator running, force an aux-heat call at the thermostat, clamp-meter the strip circuit, record zero amps. Also ask the HVAC contractor whether the iGate control or communicating thermostat has a configurable aux/emergency-heat lockout or a load-shed input — that may do it with a setting instead of a relay.
**Critical: the lockout must be manually defeatable.** A labeled switch, with written instructions: "if the heat pump itself faults during an outage, flip this and turn off the water heater." A hard-wired permanent lockout converts a compressor failure into a frozen-pipe event.
### Does locking it out leave him cold? No.
The TEV049 is a 4-ton, two-stage-scroll, vertical unit rated 56,700 BTU/hr heating at water-loop conditions, with a 50 A fuse rating. Geothermal loop conditions yield less than the WLHP figure — he should pull the performance table for his actual entering-water temperature — but for scale, his 15 kW strip package is only 15 × 3,412 = **51,180 BTU/hr**. **The compressor alone is roughly equal to the entire strip package.** Strips on a geo system are for recovery from setback and for compressor-failure backup, not for base capacity.
And the ~50 °F loop is the whole point: unlike an air-source heat pump, whose capacity collapses on the coldest night precisely when you'd need the strips most, **his ground loop doesn't care that it's 5 °F outside.** The unit makes essentially design-day capacity regardless. Locking out strips costs him *recovery speed*, not comfort.
**The free behavioral fix:** during an outage, disable thermostat setback and hold one setpoint. If you never let the house drop, you never need a recovery ramp, and the aux stages never call.
---
## 3. The flip threshold — precise numbers
### (A) Running-load threshold, strips locked out
| Unit | NG rating | NG nameplate amps | 80% design target |
|---|---|---|---|
| 22 kW | 19.5 kW | 81.25 A | **65 A** |
| 26 kW | ~22.5 kW (rated ~22.5 kW on natural gas) | 93.75 A | 75 A |
| 28 kW | 25 kW on natural gas | 104.2 A | 83 A |
> **The number: L > 65 A on natural gas → go to 26 kW. Hard stop at 81 A.**
He is at **60 A**. That is 92% of the design target — inside, but with only 5 A / 1.2 kW to spare. **One induction range, one Level 2 EV charger, one heat-pump water heater, or one added mini-split flips him over 65 A.** Also flipped by elevation above ~2,200 ft (computed above).
### (B) Auxiliary-heat kit threshold — and the decisive finding
If he wants strips available *concurrently* with his 60 A base:
| Generator (NG) | Headroom above 60 A to nameplate | Largest strip stage that fits |
|---|---|---|
| 22 kW (81.25 A) | 21.25 A = **5.1 kW** | nothing standard; **5 kW only if the water heater is shed** |
| 26 kW (93.75 A) | 33.75 A = **8.1 kW** | a **7.5 kW stage**, comfortably with water-heater shed |
| 28 kW (104.2 A) | 44.2 A = **10.6 kW** | a **10 kW stage** at nameplate |
| **Full 15 kW (62.5 A)** | **requires 122.5 A** | **no air-cooled unit exists** |
**Read that last row.** 60 A + 62.5 A = 122.5 A. The largest air-cooled generator Generac makes delivers 104.2 A on natural gas. **He is 18 A short on the top of the entire air-cooled line** — the 2025 lineup tops out at 28 kW, and past that you're into liquid-cooled territory.
**So the answer to "what aux-heat kit size flips this" is: none of them. There is no kit size at which upsizing rescues him.** Full 15 kW strip operation on generator is not purchasable at any air-cooled price point. **Lockout is mandatory regardless of which generator he buys.** That settles question 3 more cleanly than any threshold: this is a configuration problem with exactly one solution, not a sizing problem with a bigger-checkbook solution.
### (C) Where I now diverge from my own prior position
Last turn the council concluded: take the 22 kW and stop optimizing. **With 60 A on natural gas and a 15 kW strip package confirmed, I'd take the 26 kW — and not for margin anxiety.**
The reason is the specific weakness the lockout creates. Locking out all 15 kW means that if the compressor or loop pump faults during a multi-day winter outage, **he has zero heat.** Check the table: 22 kW at 60 A base leaves 5.1 kW of headroom — you cannot keep even a 5 kW strip stage alive without shedding the water heater. **26 kW leaves 8.1 kW — enough to keep a 7.5 kW emergency stage permanently available.** That is not a cushion; it is a restored function. The 26 kW is the smallest unit that lets him lock out the strips *and still have backup heat.*
Secondary: it also absorbs the elevation derate, absorbs the next electric appliance he buys, and costs nothing in gaseous-fuel engine health — the "don't oversize" rule is diesel wet-stacking advice that doesn't transfer to natural gas.
**One cost of upsizing that isn't money, and that he must check before choosing:** gas flow. The 28 kW consumes 297 ft³/hr of natural gas at 100% load; the 26 and 22 kW are lower but in the same neighborhood. If his meter and regulator are marginal for the 22 kW, upsizing makes the meter question *worse*, and a utility meter upgrade is the longest-lead item in this entire project. Resolve gas capacity before locking the kW.
---
## 4. Bottom line and the one thing in writing
**Plain language.** Your 22 kW works on natural gas: you're drawing 60 of its 81 amps, and the compressor's 104-amp start is a non-event — back the compressor's own running current out first and the worst instant is about 144 amps momentarily, during which the engine only has to make about 18 kW of the 19.5 it's rated for, and your water heater's elements actually back off on their own as the voltage dips. Starting was never your problem. Your problem is the 15 kW of strip heat, and here is the number that should decide everything: 60 amps plus 62.5 amps of strips is 122.5 amps, and the biggest air-cooled generator made delivers 104 amps on natural gas. **There is no generator you can buy that lets those strips run — so locking them out isn't a compromise, it's the only design that exists.** Locking them out won't leave you cold, because your ground loop sits near 50 °F and the compressor by itself puts out roughly what all 15 kW of strips do; just hold one thermostat setpoint during an outage instead of letting the house drop. Where I'd spend money differently: go to the 26 kW, not because 22 is too small today, but because it's the smallest unit that leaves room to keep one 7.5 kW strip stage alive — which is your only heat if the compressor itself fails in a three-day ice storm. And before you finalize any size, get the gas meter capacity answered, because that's the four-week item.
**Before you sign — and do this one first: measure, don't add.** Your 60 A is a nameplate summation, which typically runs 20–30% high because motors rarely draw nameplate and duty-cycled loads rarely coincide. Put a clamp-on energy logger on your mains for one cold week and read the actual 15-minute peak. If it logs 45–50 A, the 22 kW is comfortable and the upsize argument weakens considerably. That is a cheap measurement deciding a multi-thousand-dollar question, and no one in this thread can answer it for you.
**The single most important thing to get in writing:** a **commissioned auxiliary/emergency-heat lockout, owned end-to-end by one named contractor**, specifying (i) the device and whether the strips are on their own feeder or internal to the unit's single feeder, (ii) which stages are locked out and which remain available, (iii) a manual defeat switch, labeled, with written instructions, and (iv) an **acceptance test performed in front of you** — utility off, generator running, aux heat forced at the thermostat, clamp meter on the strip circuit reading zero. Not a verbal assurance, not "the HVAC guy will handle it." If nobody will sign that line, the sizing behind your quote is a guess, and the strips will find you on the coldest night of the year.
I am formally changing my previous stance. The Chairperson correctly pointed out that I conflated manual "unplugging" with automatic load-management modules (which the electrical code largely mandates anyway). You do not need a soft-starter to make this generator size work. The 22 kW unit is fundamentally the right machine, but the 15 kW electric heat package is a landmine.
Here is the exact arithmetic and configuration you need to make it work.
### 1. Does the 22 kW unit still work on natural gas? Yes.
**The Natural Gas Ceiling:** A 22 kW Generac produces ~19.5 kW on natural gas, giving you a hard continuous ceiling of **81 Amps**.
**(a) The Worst Continuous Case:**
Your realistic simultaneous running load is 60 A.
60 A < 81 A.
You are utilizing exactly 74% of the generator’s capacity. This is an ideal, healthy load for a standby generator running for several days. It leaves 21 Amps of headroom for transient spikes or a smaller load cycling on.
**(b) The Worst Instant (The Start):**
If the 60 A house load is running and the 104 A locked-rotor compressor surge hits:
60 A + 104 A = **164 Amps total demand for ~0.4 seconds.**
164 Amps divided by the 81 Amp rating is **2.02×** the continuous rating. Modern standby alternators are engineered to deliver 2.5× to 3× their rated current for momentary motor starts. The voltage will briefly sag, your lights might flicker, but the mass of the 999cc engine will easily drag the compressor into its running state. The 90-Amp main breaker on the generator takes minutes to trip from a thermal overload, not milliseconds; it will not care about 164 Amps for half a second.
### 2. The 15 kW Strip Heat: What happens and how to stop it
**What happens:** 15 kW of resistance heat draws **62.5 Amps**. If your thermostat calls for emergency heat while on generator power, your load jumps from 60 A to **122.5 Amps**. The generator's 90-Amp breaker will thermal-trip within a minute or two, turning off power to the entire house until you trudge outside in the cold to reset it.
**How it is prevented:** The thermostat communicates with the geothermal unit via low-voltage (24V) wires. The call for backup heat is sent on the "W2" or "Aux" terminal. To prevent this, a simple 24V "ice cube" relay is installed and connected to the auxiliary dry contacts inside the generator's automatic transfer switch (ATS). When utility power is lost, the relay opens, physically breaking the W2 signal wire. The thermostat can ask for emergency heat all it wants; the heat pump will simply ignore it.
**Whose scope of work:** This is the administrative trap. Generator installers will run the wire from the ATS to the mechanical room, but they often legally refuse to open your HVAC cabinet and splice into a communicating heat pump control board for fear of voiding your compressor warranty. **You must verify exactly who is landing those wires.** It usually requires coordinating an HVAC technician to be there on the day of the generator install.
**Will you freeze? No.**
Air-source heat pumps *need* strip heat because there is no thermal energy in 5 °F outside air, and they must run strips during defrost cycles. Your geothermal unit is pulling heat from 50 °F dirt. Your heat pump produces 100% of its rated capacity regardless of how cold the blizzard is outside. The *only* operational change is that you cannot use aggressive thermostat setbacks (e.g., dropping to 60 °F at night and asking for 70 °F in the morning) while on generator power, because the unit will be forced to recover the temperature slowly using only the compressor. Leave the thermostat at a steady temperature.
### 3. The Flip Threshold
Because your base running load is 60 A, you have exactly **21 Amps** of usable capacity left on natural gas before hitting the 81 A ceiling.
* **The Aux-Heat Threshold:** 22 kW stops being enough if your heat strips exceed **5 kW (20.8 Amps)**. Since you have a 15 kW (62.5 A) kit, you massively fail this threshold.
* **The Base-Load Threshold:** Assuming the strips are successfully locked out, the 22 kW unit becomes too small if your base running load creeps past **81 Amps**. Adding an EV charger or a hot tub would instantly break this math.
* **Why upgrading doesn't fix the strips:** Generac now makes 26 kW and 28 kW air-cooled units. A 28 kW on natural gas maxes out at 100 Amps. Your 60 A base + 62.5 A strips = 122.5 Amps. **Upgrading to the biggest air-cooled generator on the market still will not allow you to run the 15 kW strip heat.** To run the house *and* the strips, you would cross into $25,000+ liquid-cooled territory. Therefore, the lockout relay is mandatory regardless of which air-cooled size you buy.
### 4. Bottom Line Recommendation
A 22 kW unit handles your 60-amp house and starts your geothermal compressor perfectly on natural gas, provided the 15 kW backup heating element is physically disabled. Because your heat pump draws from 50-degree earth, you do not need that backup heat to stay warm; you simply have to leave your thermostat at a steady temperature during an outage. Stop worrying about the starting surge and focus entirely on ensuring the heat strips cannot activate.
**The single most important thing to get in writing:**
Look at your quote. If it does not explicitly state, *"Provide and install low-voltage lockout relay to disable geothermal auxiliary heat during generator operation, including landing wires inside HVAC air handler,"* do not sign it. Make them name exactly who is responsible for wiring the HVAC control board.
Starting anthropic/claude-opus-5
1. **Yes, 22 kW still works on natural gas for the scenario you gave — but only barely on continuous load, and it fails immediately if strip heat is allowed to come on.**
- Natural-gas continuous ceiling: **81 A at 240 V** \(\approx 19.5 kW\).
- Given running load with compressor already running and strips off: **60 A** \(\approx 14.4 kW\).
That leaves:
\[
81\text{ A} - 60\text{ A} = 21\text{ A}
\]
or about:
\[
19.5\text{ kW} - 14.4\text{ kW} = 5.1\text{ kW}
\]
of continuous margin.
For the **worst instant**, add the compressor start on top of that running load:
\[
60\text{ A} + 104\text{ A} = 164\text{ A}
\]
At 240 V, that is:
\[
164 \times 240 = 39{,}360\text{ VA} \approx 39.4\text{ kVA}
\]
That is a **momentary** surge number, not a continuous one. For the generator, the key question is whether its motor-starting capability and voltage dip tolerance can handle that extra start while already carrying 60 A. In practical standby-generator terms, a 22 kW natural-gas unit is typically expected to handle a start like this **if the rest of the house is already kept to the stated 60 A load**. The starting event is no longer the scary part; the continuous load is the real constraint.
2. **The 15 kW strip heat is the deal-breaker unless it is locked out on generator power.**
A 15 kW resistance heater at 240 V draws:
\[
15{,}000 \div 240 = 62.5\text{ A}
\]
If that energizes while the house is already sitting at **60 A**, the total becomes:
\[
60\text{ A} + 62.5\text{ A} = 122.5\text{ A}
\]
That is **well above** the 81 A continuous natural-gas ceiling. So the generator would be overloaded and either trip, sag badly, or force other loads off.
**How it is prevented:** the installer should add an **auxiliary-heat lockout relay / emergency heat lockout contactor** so the geothermal electric strips cannot energize when the house is on generator power. This is normally in the **generator installer’s scope of work**, often coordinated with the HVAC contractor because it affects the geothermal unit controls.
**Will locking it out leave him cold?** Usually no. With a geothermal heat pump and a roughly **50°F ground loop**, the compressor still has a usable heat source even in cold weather. Locking out the strips means the house may recover temperature more slowly after setback, but it does **not** mean instant loss of heat. The strips are backup comfort/recovery heat, not the primary heating source in a geo system.
3. **Flip threshold: the number that breaks 22 kW on natural gas is the aux-heat package, not the compressor surge.**
Here is the clean threshold:
- **15 kW strip package = 62.5 A**
- If those strips can run while the base house load is already around **60 A**, total demand becomes **122.5 A**, which is **far above** the 81 A natural-gas ceiling.
So the practical flip condition is:
- **If the geothermal auxiliary heat package can energize on generator power, and it is 10 kW or larger, 22 kW is already at risk; at 15 kW it is plainly too small unless locked out.**
- More precisely, with your stated **60 A running load**, the **maximum additional continuous load allowed** before hitting the natural-gas ceiling is:
\[
81\text{ A} - 60\text{ A} = 21\text{ A}
\]
That is only:
\[
21 \times 240 = 5{,}040\text{ W} \approx 5.0\text{ kW}
\]
So **any aux heat package above about 5 kW that can turn on during generator operation pushes the system over the line** at this running-load level.
That gives you the real threshold to check:
- **Running-load threshold:** if the simultaneous load with compressor running and strips off rises above **81 A**, 22 kW is not enough on natural gas.
- **Aux-heat threshold:** if a strip package of **more than ~5 kW** can energize on generator power, it breaks the current scenario.
- Since the actual installed package is **15 kW**, the only way 22 kW works is if that strip heat is **positively locked out** while on generator.
4. **Plain-language recommendation and the one thing to get in writing**
A 22 kW natural-gas standby is a workable size for this house **if** the geothermal strip heat is disabled whenever the generator is running. Your 60 A normal running load leaves about 21 A of headroom, which is enough for the compressor’s 104 A start to be a start problem rather than a sizing problem; the strip heat is the real overload risk because it adds 62.5 A all by itself. So the right move this week is to keep the 22 kW quote **only if** the installer will explicitly include a generator-operated **aux heat lockout** and confirm that the geo heat pump will still run compressor-only on outage power.
The single most important thing to get in writing is:
- **“Auxiliary/emergency electric heat will be locked out whenever the generator is supplying the house, and the generator is sized for the remaining simultaneous running load.”**
If they will not put that in writing, the 22 kW sizing is not actually confirmed yet.
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Initial responses are now shared. Each council member will critique every peer and endorse the strongest answer.
- [perplexity/sonar-pro]: STRENGTH: Solid, practical explanation of the continuous load margins and clear identification that the 15 kW strips break the math. | WEAKNESS: You fell directly into the arithmetic trap, adding the 104 A compressor surge on top of the 60 A running load without backing out the compressor's own running amps first. | FACTUAL-CONCERN: Yes, double-counting the compressor in the surge calculation overstates the worst-case transient.
- [google/gemini-3.1-pro-preview]: STRENGTH: Good translation of the lockout mechanism into physical hardware (the 24V relay on W2) and identifying the scope-of-work administrative trap. | WEAKNESS: I made the exact same embarrassing double-counting math error as Sonar, adding inrush to a running load that already contained the compressor. | FACTUAL-CONCERN: Yes, 60 A + 104 A = 164 A is physically impossible because a compressor cannot start and run simultaneously.
- [anthropic/claude-opus-5]: STRENGTH: Masterclass response. Caught the double-counting trap, added the brilliant insight about resistive loads self-shedding during voltage sag, and provided a highly defensible reason to upgrade to 26 kW. | WEAKNESS: The elevation formula math is slightly dense for a homeowner, but the conclusion is sound. | FACTUAL-CONCERN: No.
I am endorsing Claude-Opus-5 because it caught the glaring math error the rest of us made, and its recommendation to upsize to 26 kW specifically to keep half the emergency strips alive is the kind of system-level thinking that actually saves a homeowner in an ice storm. The council missed the physical gas plumbing—while we all warned about the meter, a 300 CFH generator is highly sensitive to the pipe diameter and run length between the meter and the unit, which installers frequently undersize to save money.
**perplexity/sonar-pro**: STRENGTH: Cleanest, shortest statement of the single decisive inequality (60 + 62.5 = 122.5 A against an 81 A ceiling) and the correct "5 kW is all the headroom you have" conversion. WEAKNESS: It never answers question 3 as asked — the homeowner explicitly named the 26 and 28 kW units and asked at what point he is pushed up; Perplexity never mentions either model or their natural-gas ratings, so the one number requested is absent. It also calls 74% loading "only barely" adequate in item 1 and then calls the same 21 A "enough" in item 4. FACTUAL-CONCERN: yes — it puts the aux-heat lockout "normally in the generator installer's scope of work," which is the exact misconception that causes the work not to get done; the generator installer owns the transfer-switch contact, not the terminals on a communicating ClimateMaster board.
**google/gemini-3.1-pro-preview**: STRENGTH: The genuinely load-bearing finding, stated more bluntly than anyone: upsizing does not rescue the strips, so the lockout relay is mandatory at every size — which correctly converts this from a sizing question into a configuration question. Also the only peer to name the behavioral cost precisely (no aggressive setback while on generator). WEAKNESS: It commits the double-count. The 60 A was given as "with the compressor running," so 60 + 104 = 164 A adds the compressor's running amps to its own inrush; the worst instant is roughly 40 + 104 = 144 A. The 2.02× ratio is therefore inflated, and it is asserted against a "2.5–3×" rule the council already admitted it cannot verify for this machine. FACTUAL-CONCERN: yes, two: the 164 A figure, and "28 kW on natural gas maxes out at 100 Amps" — retailer spec listings put the 26 kW at 22,500 W NG (NG Power Capacity: 22,500 Watts, i.e. 93.75 A), which makes the 28 kW's NG figure higher than 100 A, not equal to it. The conclusion survives; the number should not be quoted to an installer. Also "produces 100% of its rated capacity regardless" overstates real geo behavior — entering water temperature does fall over a long heating season.
**anthropic/claude-opus-5**: STRENGTH: The only answer that got the worst-instant arithmetic right by backing the compressor's RLA out first, and the only one to notice that resistive load self-sheds as V² during the sag — which means the naive amp addition is wrong in the homeowner's favor. The staged-lockout configuration (keep stage 1, interlock it against the water heater) is the single best engineering idea produced this turn. The commissioning test, the manual defeat switch, and "measure with a logger, don't sum nameplates" are all correct and actionable. WEAKNESS — and this is my substantive disagreement: the 26 kW recommendation is refuted by its own table. Opus justifies upsizing because 22 kW leaves only 5.1 kW of headroom, too little to keep an emergency strip stage alive. But the emergency case *is* compressor failure, and a failed compressor is not drawing its ~20 A. Base 60 A − 20 A compressor − 18.8 A water heater (already on a management module per the prior turn) = ~21 A, which leaves room for a **10 kW** stage (41.7 A) at ~63 A total — under the 65 A design target, on the 22 kW. The one scenario invoked to justify spending more is the one scenario that frees the most capacity. FACTUAL-CONCERN: yes — it cites 297 ft³/hr for the 28 kW, while a retailer listing shows NG Fuel Consumption @ 100% Load: 333 ft3/hr for the smaller 26 kW. One of those is misattributed, and since Opus correctly calls the gas meter the long-lead item, quoting a low CFH number is the wrong error to make. Its 22.5 kW / 93.75 A figure for the 26 kW NG rating does check out, though note some sources cite 24 kW NG depending on model year — so he must read his own spec sheet, not a table from this council.
**Why I endorsed Opus**: it is the only response whose question-1(b) arithmetic is defensible, and it is grounded in the actual spec-sheet language that governs the margin debate — standby is applicable for the duration of the outage, and no overload capability is available for this rating, plus the ~3.5% per 1,000 ft derate. I endorse it while rejecting its headline recommendation: on these numbers the answer is stay at 22 kW, add a two-stage lockout that preserves one strip stage, and put the upsize money into the gas meter and a week of logged mains data. **What the council collectively missed**: every answer treated the 104 A compressor as the only start event, but the well pump inside that 60 A has its own locked rotor (commonly 30–60 A) and can start while the compressor runs — nobody asked whether the two can coincide, and nobody asked whether the loop pump/flow center sits on a backed-up circuit, which decides whether the compressor can run at all.
[anthropic/claude-opus-5]: STRENGTH: Best at separating starting from carrying load, and it flags the 15 kW strip heat as the true sizing constraint. | WEAKNESS: It overreaches on exact trip/breaker behavior and adds some speculative details about the heat pump package. | FACTUAL-CONCERN: yes — several specific breaker/current and product-configuration claims are asserted without verification.
[google/gemini-3.1-pro-preview]: STRENGTH: Clear arithmetic and it correctly identifies the natural-gas ceiling versus the 60 A running load. | WEAKNESS: It gives a wrong or unsupported claim that the 164 A start will trip the generator in a minute or two, which overstates the risk and muddles surge vs continuous behavior. | FACTUAL-CONCERN: yes — the breaker-trip timing and some surge-capacity statements are not grounded in verified Generac data.
[perplexity/sonar-pro]: STRENGTH: It correctly says 22 kW works on natural gas for the worked example only if strip heat is locked out. | WEAKNESS: It is too conservative in implying the start is the main issue early on, then later proves the opposite; its relay-scope explanation is also too generic. | FACTUAL-CONCERN: yes — the 240 V load math is fine, but the “typically expected” generator-start handling is not verified for the exact model.
I endorsed anthropic/claude-opus-5 because it best identifies the actual fault line: continuous load, not compressor inrush. I declined the others because they either overstate trip risk or leave the configuration question too loose; the council collectively still didn’t pin down whether the aux heat is staged and therefore could be partially preserved instead of fully locked out.
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anthropic/claude-opus-5 serves as Chairperson and will now synthesize the council's reasoning into a single canonical answer.
# Chairperson's verdict: stay at 22 kW — and change the control logic, not the generator
The council unanimously endorsed an answer that recommended upsizing to 26 kW. **I'm overriding that.** The upsize was justified by one scenario — "if the compressor fails in an ice storm, a full lockout leaves you with zero heat" — and that scenario is the one that *frees* the most capacity, because a failed compressor isn't drawing its 20 amps. The fix costs nothing: make the lockout **state-aware** instead of blanket. Details below.
---
## 1. Does 22 kW still work on natural gas? Yes.
### (a) Worst continuous case
Nameplate: 19,500 ÷ 240 = **81.25 A**. His load: **60 A**.
> 60 ÷ 81.25 = **73.8% of nameplate** · headroom **21.25 A / 5.1 kW**
> Against an 80% prudence target (65 A): **5 A / 1.2 kW to spare**
Why the 80% target isn't optional here: Generac's own 22–28 kW sheet defines standby as applicable for supplying emergency power for the duration of the utility power outage, with no overload capability available for this rating, and warns that maximum kVA and current are limited by fuel BTU content, ambient temperature, humidity, barometric pressure and altitude, with maximum power decreasing roughly 3.5% per 1,000 ft above sea level and about 1% per 10 °F. 81.25 A is a wall, not a soft limit.
**Elevation flip point, exactly:** 19.5 × (1 − 0.035h) × 0.80 ÷ 0.24 ≥ 60 → **h ≤ ~2,200 ft.** Above that, 60 A no longer fits the 80% target. Check your elevation on your phone; it's a one-minute answer.
### (b) Worst instant — and the arithmetic error to reject
60 + 104 = 164 A is **wrong**, and two council members did it. His 60 A was stated *with the compressor running*. A compressor cannot start and run simultaneously; back its own running amps out first.
> RLA at 104 LRA on a two-stage scroll ≈ 18–22 A; call it 20.
> Base with compressor off: 60 − 20 = **40 A**
> Worst instant: 40 + 104 = **144 A** (1.77× nameplate, momentary)
**Real-power check — what the engine feels.** Locked-rotor current is almost entirely reactive (a stalled induction motor is electrically a shorted transformer), so power factor at start runs ~0.30–0.40:
> Inrush: 104 × 240 = 25.0 kVA × 0.35 ≈ **8.8 kW**
> Rest of house: 40 × 240 × 0.95 ≈ **9.1 kW**
> **Total ≈ 17.9 kW against 19.5 kW = 92%.** The engine never exceeds its rating.
**The cushion the amp-addition method throws away:** resistance loads are constant-*impedance*, so their draw falls as V². During a 15% voltage dip his water heater and oven elements back off by 1 − 0.85² = **28% on their own**, at precisely the instant he needs it.
**The start event nobody computed — and it's the real worst case.** Everyone treated the compressor as the only motor. His **well pump** is inside that 60 A at ~9 A running, with its own locked rotor (commonly 40–50 A for a 1 hp submersible — verify the nameplate). If both start together:
> Base excluding both: 60 − 20 − 9 = 31 A → ~7.1 kW real
> Compressor inrush 8.8 kW + well pump (50 A × 240 × 0.4 pf) 4.8 kW
> **≈ 20.7 kW real, or 106% of rating, for a few tenths of a second.** Survivable; not comfortable.
Two free mitigations: the geo's anti-short-cycle timer staggers restarts naturally, and — the cheap one — **check your well pressure tank's precharge (typically ~2 psi below cut-in).** A waterlogged tank makes the pump cycle every few seconds, which is what turns a rare coincidence into a nightly one. That's a $0–200 fix for the only genuinely marginal transient in this house.
**On Generac's motor-starting spec:** it exists as a published line — Generac advertises the 26 kW's new alternator design that produces 230 LRA or 55.2 kVA starting power. I still can't verify the 22 kW row. **Ask for it by model number** rather than accepting "it'll be fine."
---
## 2. The 15 kW strip heat: what happens, and the device
### If it energizes on generator
> 60 A + 62.5 A = **122.5 A = 29.4 kW demanded vs 19.5 kW available = 151%**
The 999 cc engine physically cannot make that. Sequence: engine lugs → frequency droops → voltage collapses → controller alarms on overload/underfrequency and/or the ~90 A main breaker trips thermally. The spec sheet's "no overload capability" language means there is no ride-through. Worse, it **oscillates**: strips call → generator drops → house de-energizes → thermostat gets colder → strips call harder. Some overload states latch and need a manual reset. Real-world outcome: a dark, cold house during exactly the storm he bought the generator for.
### The device — and the question that picks it
**Confirm first: are the strips on their own feeder/breaker, or fed internally off the unit's single MCA?** Nobody on the council pinned this down, and it determines everything:
- **Separate strip feeder:** a load-management module on that breaker is legitimate and simple.
- **Single internal feeder:** a power-side shed module **must not be used** — shedding it kills compressor and blower too, leaving no heat at all. The correct device is a **signal-level interlock**: a relay interrupting the auxiliary-heat *call* (W2 / aux terminal or heat-relay coil at the iGate board), driven by a generator-running contact at the transfer switch. Also ask whether the iGate control or communicating thermostat has a configurable aux-lockout or load-shed input — that may do it with a setting instead of hardware.
**The scope seam, named:** the transfer-switch auxiliary contact belongs to the generator installer; the aux-heat terminal at the ClimateMaster board belongs to the HVAC contractor. **The conductor between them belongs to nobody, which is why it doesn't get installed.**
### Does locking it out leave him cold? No.
His 15 kW package is 15 × 3,412 = **51,180 BTU/hr**. A 4-ton TEV049 produces roughly that much heating on its own. More important: unlike an air-source heat pump, whose capacity collapses on the coldest night precisely when strips matter most, **his ~50 °F ground loop doesn't care that it's 5 °F outside.** Locking out strips costs *recovery speed*, not comfort. Free behavioral fix: hold one setpoint during an outage instead of using setback, and the aux stages never call.
---
## 3. The flip threshold — and the resolution of the 22-vs-26 argument
### Running load (strips locked out)
| Unit | NG rating | NG amps | 80% target |
|---|---|---|---|
| 22 kW | 19.5 kW | 81.25 A | **65 A** |
| 26 kW | 22.5 kW NG / 26 kW LPG (some listings cite up to 24 kW by model year) | ~93.75 A | ~75 A |
| 28 kW | read the sheet — council figures conflicted | — | — |
> **The number: L > 65 A on natural gas → go up a size. Hard wall at 81.25 A.**
He's at 60 A: inside, with 5 A to spare. **One induction range, one Level 2 EV charger, one heat-pump water heater, or one added mini-split flips him.** So does elevation above ~2,200 ft.
### Aux-heat kit size: there is no size at which upsizing rescues the strips
60 + 62.5 = **122.5 A.** The largest air-cooled unit delivers roughly 94–104 A on natural gas. **Full 15 kW concurrent strip operation is not purchasable at any air-cooled size.** Lockout is mandatory regardless of what he buys. Question 3's honest answer: *any* package above ~5 kW breaks concurrency at a 60 A base (81.25 − 60 = 21.25 A = 5.1 kW), and no upsize fixes it.
### The distinction that settles it: AUX heat ≠ EMERGENCY heat
These are two different signals in a heat pump, and the council treated them as one. **Aux** = strips *plus* compressor (setback recovery). **Emergency** = compressor disabled, strips alone (compressor has faulted). Their load arithmetic is completely different:
| Mode on generator | Math | 22 kW? |
|---|---|---|
| Aux: compressor + 5 kW stage, water heater shed | 60 − 18.8 + 20.8 = **62.0 A** | ✅ |
| Aux: compressor + 10 kW stage | 60 + 41.7 = 101.7 A | ❌ |
| **Emergency: compressor faulted (−20 A), water heater shed, 10 kW stage** | 60 − 20 − 18.8 + 41.7 = **62.9 A** | ✅ |
| Emergency: full 15 kW, water heater shed | = 83.7 A | ❌ even on 22; marginal on 26 |
**So the correct configuration on the 22 kW is a three-tier interlock:** block all aux stages by default; permit *one 5 kW stage* interlocked against the water heater if he wants faster recovery; and permit *up to a 10 kW stage in emergency mode only*, when the compressor is off. He gets genuine compressor-failure backup heat **on the 22 kW**, which is the entire function the 26 kW was being purchased to restore. Save the money; spend it on the interlock and the gas supply.
*This design depends on two facts to verify:* the 15 kW package must be **staged** (typically 5+10 or 7.5+7.5) and the stages independently controllable. If it's a single indivisible 15 kW block, no air-cooled generator carries it — then the answer is a **labeled manual defeat switch** with written instructions ("compressor failed: flip this, turn off the water heater"), which is acceptable because it's a rare failure case, not a nightly one.
### The gas-supply item, with the council's numbers corrected
Upsizing makes the long-lead problem **worse**: one distributor listing puts the 26 kW at 333 ft³/hr natural gas at 100% load — higher than the ~297 figure quoted in deliberation. And the constraint isn't only the meter: Generac's sheets state that fuel piping must be sized for full load, with natural-gas inlet pressure of 3.5–7 inches of water column. **Pipe diameter and run length between meter and unit are routinely undersized to save money.** Demand a written gas load calculation (pipe size vs. equivalent length, all existing appliances included) and a **commissioning measurement of delivered inlet pressure at 100% load with a manometer.** A gas-starved generator sags exactly when the compressor kicks in — and gets misdiagnosed as "too small" for years.
*One credibility note:* a distributor FAQ in current circulation states "Natural Gas: 22500 Watts ÷ 240 Volts = 46.9 Amps" — that's 22,500 ÷ 480. Third-party generator data is error-riddled. **Read your own spec sheet.**
---
## 4. What to do this week
**Plain language.** Your 22 kW works on natural gas. You're drawing 60 of its 81 amps, and the 104-amp compressor start is a non-event: back the compressor's own running current out first and the worst instant is about 144 amps momentarily, during which the engine only has to make about 18 of its 19.5 kW — and your water heater elements actually back off by themselves as the voltage dips. Don't buy a bigger generator. Your 15 kW of strip heat is the whole problem: 60 amps plus 62.5 amps is 122.5 amps, and the biggest air-cooled unit made delivers roughly 94 to 104 on natural gas, so **no generator you can buy will run those strips** — the lockout isn't a compromise, it's the only design that exists. It won't leave you cold, because your ground loop sits near 50 °F and the compressor alone puts out about what all 15 kW of strips do; just hold one thermostat setpoint during an outage instead of letting the house drop. Then ask for the one thing the whole council underspecified: don't lock the strips out *blindly*, lock out the aux-with-compressor call but leave one 10 kW stage available in emergency mode only, when the compressor is off and not drawing its 20 amps. That arithmetic (63 amps) fits your 22 kW and gives you real backup heat if the compressor itself dies. Before you finalize anything, put a clamp-on logger on your mains for one cold week — your 60 A is a nameplate sum, which typically runs 20–30% high. If it logs 45–50 A you're comfortable; if it logs 68 A or more, revisit the size.
**Get in writing — one item, four parts.** A **commissioned auxiliary-heat interlock owned end-to-end by one named contractor**, specifying: (i) whether the strips are on their own feeder or internal to the unit's single feeder, and which device is therefore used; (ii) **which stages are blocked and which remain available in emergency mode** — not "aux heat disabled," that phrasing is what strands you without heat; (iii) a **labeled manual defeat switch** with written instructions; and (iv) an **acceptance test in front of you**: utility off, generator running, aux heat forced at the thermostat, clamp meter on the strip circuit reading zero. If no one will sign that line, the sizing behind your quote is a guess.
**Two more nameplate reads, both cheap:** confirm the **loop pump / flow center circuit is on the backed-up side and not on a shed module** (lose flow, the compressor faults and your heat pump is decorative), and read the **well pump's LRA** so the compound-start number above stops being an estimate.
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anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
anthropic/claude-opus-5 is thinking...
Published example by Shingikai, run September 17, 2026, using anthropic/claude-opus-5, google/gemini-3.1-pro-preview, perplexity/sonar-pro.
Models: anthropic/claude-opus-5, google/gemini-3.1-pro-preview, perplexity/sonar-pro
You asked whether a 22 kW generator can start your geothermal heat pump's 104-amp compressor. It can, easily, and that is the wrong thing to be worried about. The question that actually decides whether this install works is one you didn't ask: what happens to your electric backup heat when the power is out.
We ran your situation past three separately trained AI models — Claude Opus 5, Google's Gemini 3.1 Pro, and Perplexity's Sonar — over two rounds, under a chairperson format where each answers alone, critiques the others, and one synthesizes. They agreed the compressor surge is a non-event, then spent the rest of their time on the load nobody quotes: the electric resistance strip heat that lives inside that same geothermal cabinet.
Short version: the 22 kW is very likely the right size. Don't let anyone sell you a bigger one to "handle the surge." Put that attention into how the strip heat gets locked out instead.
Your numbers, unchanged: a quote for a 22 kW Generac, a mostly-electric house, a ClimateMaster TEV49 geothermal unit with a 104-amp compressor startup, and a goal of not having to unplug or shed anything during an outage, though you don't need the oven and the dryer running at once.
The assumptions we added, labeled as assumptions: 240 V single-phase service, and a 22 kW unit's continuous output of about 81 amps on natural gas and 92 amps on propane (that pair is off Generac's own spec sheet, not a guess). For the second round we handed the council a worked example to stress-test the answer — natural gas, a 15 kW backup-heat package, and a roughly 60-amp running load. Those three numbers are illustrative. We do not know your fuel, your heat-kit size, or your real load, and nothing below assumes we do. The point of the page is to hand you the method and the thresholds so you can drop in your own nameplate readings.
We reproduced every headline number in a script before trusting the models.
The 104-amp scare dissolves under one distinction: amps are not kilowatts. A 104-amp locked-rotor surge is 104 × 240 = 25 kVA of apparent power, which looks fatal next to "22 kW." But locked-rotor current is almost entirely reactive — a stalled motor is electrically a shorted transformer — so at a starting power factor near 0.35 the engine only feels about 8.8 kW of real power, for well under a second. Set it against the generator's own 100-amp main breaker: 104 amps is 1.04× the breaker rating, which takes minutes to trip, not the half-second a start lasts. The instantaneous magnetic trip sits near 900 amps. Your surge is nowhere near either mechanism.
The number that actually binds is what you carry for days, not what you start for a second. On natural gas that wall is about 81 amps.
| Question | Worked-example math | Result |
|---|---|---|
| Continuous load | 60 A carried vs 81 A natural-gas ceiling | 74% loaded — healthy |
| Worst instant (a start) | back out the compressor's own ~20 A running first: 40 A base + 104 A inrush | 144 A momentary, not 164 |
| Engine's real-power view | 8.8 kW inrush + 9.1 kW rest of house | 17.9 kW of a 19.5 kW rating — 92% |
| 15 kW strips energize | 60 A + 62.5 A | 122.5 A — over the wall |
That last row is the whole story. Fifteen kilowatts of strip heat is 62.5 amps. Add it to a 60-amp house and you need 122.5 amps — and even the largest air-cooled home standby made, the 28 kW, delivers only about 104 amps on natural gas. There is no air-cooled generator you can buy that will run a large strip package on top of your house. So the strips have to be locked out whenever you're on generator power, whatever size you buy. That single fact converts this from a sizing question into a wiring question.
A soft starter on the compressor would cut that 104-amp surge by half or more. But the surge was never the problem, so buy one for reduced flicker and compressor longevity if you like it on its own merits, not to make the generator work.
Two disagreements, both worth seeing.
In round two, both Gemini and Sonar added the 104-amp compressor start on top of the 60-amp running load to get 164 amps. Opus caught it: the 60 already includes the compressor running, and a motor cannot start and run at the same instant, so you back its roughly 20 running amps out first and the worst instant is 144, not 164. Gemini owned the mistake on the record — "a compressor cannot start and run simultaneously."
The larger split: at one point all three models endorsed stepping up to a 26 kW, on the logic that 22 kW leaves too little headroom to keep a backup-heat stage alive if the compressor itself fails in an ice storm. Then Opus overrode the room, including its own earlier vote, with the point that demolished the upsell: the emergency case is a failed compressor, and a failed compressor is not drawing its 20 amps — which frees exactly the capacity needed to keep a strip stage running on the 22 kW. The bigger generator was being justified by the one scenario that makes it unnecessary.
This is where a single model would have steered you wrong. Asked cold, Gemini's first answer called the 104-amp surge a "massive risk" and a soft starter "practically mandatory" — built on a physics slip, treating 25 kVA of reactive inrush as 25 kW of real engine load. Sonar's solo answer was competent but generic and leaned on a couple of low-quality web sources. Opus was the seat that got the physics right, named the strip heat that the other two models and your original thread all walked past, caught the double-count the other two made, and then reversed a unanimous upsell.
Honest read: this was not three models converging on the right answer. It was one strong seat carrying the correctness, with Gemini's willingness to change its mind on the record — twice — and Sonar's blunt "the strips, not the compressor, are the killer" sharpening it. Gemini also added the most useful real-world catch of the run: generator installers often won't open an HVAC control board, which is the exact reason the lockout wire ends up installed by nobody.
Handing the council a concrete nameplate reading is what surfaced the real answer. The compressor question closed, the strip-heat question opened, and the resolution turned on a distinction the first round missed: aux heat and emergency heat are two different signals in a heat pump. Aux heat is strips plus the compressor, for fast recovery from a setback. Emergency heat is strips alone, when the compressor has faulted. A blanket "disable aux heat" lockout strands you with no heat if the compressor dies. A state-aware interlock — block the aux stages by default, but allow one stage in emergency-only mode, when the compressor is off and not drawing its 20 amps — keeps genuine backup heat available on the 22 kW. That is the function the 26 kW was being bought to restore, delivered for the price of a relay instead.
And locking the strips out does not leave you cold. Fifteen kilowatts of resistance heat is about 51,000 BTU/hr; a 4-ton geothermal compressor puts out roughly that much on its own. Unlike an air-source heat pump, whose capacity collapses on the coldest night exactly when the strips matter most, your ground loop sits near 50 degrees and does not care that it is 5 degrees outside. Locking out the strips costs recovery speed, not comfort. Hold one thermostat setpoint during an outage instead of letting the house drop, and the aux stages never call in the first place.
Five things to pull or confirm, in order.
Read the geo nameplate and model number for two figures: the electric backup-heat package in kW (this is the number that drives the whole decision) and the compressor's running amps. Convert kW to amps with kW × 1000 ÷ 240 — so 10 kW is 42 amps, 15 kW is 62.5, 20 kW is 83.
State your fuel. Natural gas or propane is an 11% swing, 81 amps versus 92, and it moves every threshold above.
Get the strip-heat lockout in writing, owned end to end by one named contractor, specifying: whether the strips are on their own breaker or fed inside the unit; which stages are blocked and which stay available in emergency-only mode (not just "aux heat disabled" — that phrasing is what leaves you cold); a labeled manual-override switch with instructions; and an acceptance test done in front of you, with utility off and the generator running, forcing an aux-heat call and clamping the strip circuit to confirm zero amps.
Before you lock in the size, put a clamp-on logger on your mains for one cold week. Your load figure is a nameplate sum, which typically runs 20 to 30% high. If the real peak logs 45 to 50 amps, the 22 kW is comfortable; if it creeps past about 65, revisit.
Confirm the two things the whole plan quietly depends on: that the gas meter and the pipe run can actually feed the generator (a 22 kW pulls about 300 cubic feet an hour at full load, and a gas-starved unit sags precisely when the compressor kicks in, then gets misdiagnosed as too small for years), and that the geo's loop pump is on a backed-up circuit, because if it loses flow the compressor faults and the heat pump is decorative. There is also a code angle — a whole-house automatic transfer switch has to satisfy the load rules in NEC 702 — so ask your installer whether your calculated load requires managed load-shedding regardless of what you prefer.
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