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What size generator to run heat pump

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The short answer

What size generator to run heat pump? A generator size for a heat pump comes from exact outdoor and indoor unit documents. Add all running loads and the correct startup gaps. Include any auxiliary heat that may run, and match voltage at the chosen fuel. If any of that data is missing, the size stays unknown.

Last updated October 2026

What's covered11

Picking a generator for a heat pump is not a guess. The answer comes from the unit's own papers. This guide shows which numbers to find and how to add them. It also shows when the data is too thin to give an answer.

To size a generator for a heat pump, read the outdoor and indoor unit documents. Add the running watts of everything that will run at once. Then add the right startup gap for that same unit. Count any auxiliary heat that may run, and match the voltage. If a needed number is missing, the size cannot be confirmed yet.

Quick comparison of published generator data

This table lists maker figures for the models in this guide. It shows output and voltage only. It does not prove that any model fits a heat pump. You still need the heat pump data, a startup total, the receptacle and connection gear, and the runtime you need.

Model Published voltage Running or rated output by fuel
Honda EU2200i 120 V 1800 W rated, 2200 W maximum (gasoline)
Honda EU3200i 120 V 2600 W rated, 3200 W maximum
Honda EU3000iS 120 V 2800 W rated, 3000 W maximum
Champion 201278 120 V Gasoline 3500 W, propane 3150 W
Champion 201176 120/240 V Gasoline 7250 W, propane 6525 W, natural gas 5875 W
Westinghouse WGen11500TFc 120/240 V Gasoline 11,500 W, propane 10,500 W, natural gas 9,500 W
DuroMax XP13000HXT 120/240 V Gasoline 10,500 W, propane 10,000 W, natural gas 9,000 W
Generac Guardian 26 kW 240 V rated Propane 26 kW, natural gas 22.5 kW maximum continuous
KOHLER 20RCA 120/240 V option Propane 20 kW, natural gas 18 kW
Cummins RS20A 120/240 V Propane 20 kW, natural gas 18 kW
BLUETTI AC200L 120 V 2,400 W rated AC, 2,048 Wh stored
Jackery Explorer 2000 v2 120 V 2,200 W rated AC, 2,042 Wh stored

Match your unit's label and manual revision before sizing loads. Starting watts do not promise a motor will start or state how long peak output lasts.

What size generator to run heat pump: start with exact unit documents

A split heat pump has an outdoor unit and an indoor unit. Each one has its own model number and nameplate. Find both. Then look for the maker's data sheet or install manual for each exact model.

You need several facts from those papers. Note the running load of each part and the voltage it needs. Note any published starting figure. Check whether auxiliary heat is installed and how large it is.

Write down which parts can run at the same time.

Nameplates may list amps and volts instead of watts. Volts times amps gives volt-amps, which is apparent power. It equals watts only when the power factor is known. If the papers do not give a power factor or a watt figure, do not treat volt-amps as watts.

Why tonnage shortcuts and soft-start guesses fail

Tonnage describes heating and cooling capacity. It does not tell you the electric draw. Two units with the same tonnage can use different parts. So a chart that turns tons into watts can be wrong for your unit.

Soft starters raise the same problem. Some systems may have one, and some may not. Even when one is present, its effect depends on the exact device and unit. Use a reduced starting figure only when the documents for your installed parts give it.

A variable-speed compressor can change its draw during a cycle. One nameplate figure may not show every moment. That is one more reason to use the maker's own data and not a general rule.

Startup demand: adding it the right way

First find R. R is the running watts of everything that will be on at once. Include the outdoor unit, the indoor unit, any auxiliary heat that may run, and every other load you plan to power.

Next find each motor's gap. A gap is one unit's starting watts minus that same unit's running watts. Treat a negative gap as zero. If only one unit can start at a time, add the largest single gap to R.

That gives your startup total, S.

If units may start together, add every gap that could happen at once. Count each start. Do not assume motors never start together. Your controls and loads decide that, not a rule of thumb.

Two mistakes are common. Some people add a full starting figure on top of R. That counts the same motor twice. Others leave a motor's running watts out of R and add only its gap.

That undercounts. Our guide on running wattage vs starting wattage explains the split in more detail.

Then compare. R must fit the generator's running or rated output at your fuel. S must fit its published starting or maximum output. If the heat pump papers list no starting figure, S is unknown.

In that case, the generator size is unknown too.

Auxiliary heat can change the answer

Many heat pumps can have electric auxiliary or emergency heat. This is a separate load from the compressor and fans. Its rating should appear on its own nameplate or in the indoor unit documents.

If that heat may turn on during an outage, add its running watts to R. If your setup keeps it off, you may leave it out. Your thermostat and system papers tell you which case applies. Do not guess its size from tonnage.

Voltage, fuel and connection checks for a heat pump generator

Check voltage before you do any wattage math. Read the voltage each heat pump part needs from its own papers. Then match it to what the generator publishes. A large watt figure cannot make up for the wrong voltage.

The three Honda models, the Champion 201278 and the Westinghouse iGen2550DFc list 120 V output. The Champion 201176, Westinghouse WGen11500TFc and DuroMax XP13000HXT list 120/240 V. The Generac Guardian 26 kW lists 240 V rated output. An adapter cannot create a voltage the generator does not make.

Fuel changes the usable output on these listed models. The WGen11500TFc drops from 11,500 W running on gasoline to 9,500 W on natural gas. The Champion 201176 also runs on natural gas, at 5875 W. Size with the rating for the fuel you will use.

Fuel pressure and flow are a separate check. You cannot work them out from electric watts.

A receptacle type alone does not prove home use. The iGen2550DFc has an RV TT-30R outlet, and its page says it is not transfer-switch-ready. Still, 120 V output alone does not rule out every transfer system.

The connection gear must match too. The Reliance 306CRK kit holds a six-circuit 30 A switch, an inlet and a ten-foot cord. Generac model 6853 is a 30 A pre-wired manual transfer switch kit. Those lists show what each kit contains.

They do not prove fit with your panel or your heat pump circuit. The generator, switch, inlet, panel and circuits must all match. A licensed electrician installs the gear under local codes.

The WGen11500TFc page also describes pairing with a WATS200 automatic transfer system. This guide does not compare that system's full needs. Treat automatic operation as unresolved until you have exact matching documents.

Standby units list a single output per fuel. The KOHLER 20RCA lists its automatic transfer switch as a separate option. Model documents must confirm the exact order. A standby rating still has to cover your R and S at the fuel you use.

Battery power stations: power versus energy

Watts measure power at one moment. Watt-hours measure stored energy. The BLUETTI AC200L lists 2,048 Wh and 2,400 W rated AC output. The Jackery Explorer 2000 v2 lists 2,042 Wh and 2,200 W.

Both list 120 V US outlets. So check your heat pump's voltage first. Then check R and S against the rated output. To estimate runtime, divide the stored watt-hours by your running watts.

This gives hours under steady load, and it is only a rough figure.

Safe placement

CPSC says portable engine generators belong outdoors. Keep them at least 20 feet from homes, with exhaust pointed away. Never run one indoors or in a garage, even with the doors open. Use CO alarms, and get to fresh air if one sounds.

CPSC also says to run a generator on a dry surface. Shut it off and let it cool before refueling. Never backfeed through a wall outlet. A standby unit's clearances come from its own manual and local rules.

Even an automatic setup still needs safe outdoor placement.

If you are planning other loads, see what size generator to run refrigerator and freezer. For the full process, start at what size generator do I need.

Sources, method and limitations

Every generator figure here comes from a maker's product page, spec sheet or brochure. Safety rules come from CPSC. The definitions of power and energy come from the US Department of Energy style guide.

Heat pump ratings vary by unit, so this guide gives no size for any model. Use your unit's nameplate for running and starting figures. Runtime figures are tied to each maker's test loads. Do not apply them to a heat pump that cycles on and off.

A generator's output alone is never a full fit result.

What size generator to run heat pump FAQs

How do I find my heat pump's running load?

Look for the nameplate on the outdoor unit and the indoor unit. Then find the maker's data sheet for both model numbers. Nameplates may list amps and volts. Volts times amps gives volt-amps, not watts, unless the power factor is known.

If a figure is missing, the size stays unknown.

Can a 120 V inverter generator run a heat pump?

Only if every part you plan to run is documented for 120 V. The Honda EU2200i, EU3200i and EU3000iS list 120 V output. An adapter cannot create a missing 240 V output. If the unit data sheet calls for 240 V, you need a source that publishes 240 V.

Does fuel choice change generator size?

It can for the listed models. The Champion 201176 lists 7250 W running on gasoline, 6525 W on propane and 5875 W on natural gas. The Generac Guardian 26 kW lists 26 kW on propane and 22.5 kW on natural gas. Use the rating for the fuel you will actually use.

Does a transfer switch kit make a generator fit?

No. A kit listing tells you what is in the box. The Reliance 306CRK has a switch, inlet and cord, but that is not proof of fit. The generator, switch, inlet, panel and circuits must all match.

A licensed electrician installs it under local codes.

Primary documents

What size generator to run heat pump Verdict

What size generator to run heat pump? Start with exact outdoor and indoor unit documents, not tonnage. Put all running loads into R, including any auxiliary heat that may run. Add the correct startup gaps to get S.

Then match R, S and voltage to a generator's ratings at your chosen fuel.

If a model meets all of those checks, it is a fair candidate. Its receptacle, connection gear and runtime still need review. If any heat pump figure is missing, the size cannot be confirmed yet.

Continue your backup plan

Choose your next step

Once you have a size, read the generator sizing guide and follow its link to the home generator picks. Match the exact fuel, voltage and starting limits to your result before you choose.