What Size Generator Do I Need to Run a Window Air Conditioner?

The compressor restarts through the day, so the start has to clear every cycle.

Quick answer: Honda lists a 10k BTU window air conditioner at 1,500 running watts and 2,200 starting watts, and Champion lists that size at 900–1,200 running watts and 1,800–2,400 starting watts. Covering both charts takes a running rating that clears 1,500 W and a starting rating that clears 2,400 W. A Honda EU2200i maximum of 2,200 W matches Honda's start but is short of Champion's 2,400 W start, while the Champion manual lists 5,000 W running and 6,250 W starting, which covers either chart.

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Running and starting watts

Load	Running watts	Starting watts	Source
Window AC, 5k BTU	450–600	900–1,200	Champion
Window AC, 10k BTU	900–1,200	1,800–2,400	Champion
Window AC, 10k BTU	1,500	2,200	Honda

Honda's wattage guide lists starting watts, then running watts. Champion's chart lists running watts, then starting watts. This table puts every figure in the Running and Starting columns. Not listed means that source does not give a separate starting figure.

How to size it

Add the running watts of every load that will be on together, then add the single highest starting surge (Generac; Honda). Generac notes that starting watts are often 2–3 times running watts, and that standby units should get a dealer survey.

A 5k BTU unit is a smaller load: Champion lists 450–600 running watts and 900–1,200 starting watts, which fits under the EU2200i rated output of 1,800 W and maximum of 2,200 W. Two EU2200i units can run in parallel for up to 4,400 W, which also covers a 10k BTU start of 2,400 W.

Check a full load list on the generator size calculator.

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Run the generator outdoors only, 20 ft from the house (CPSC).

FAQ

Can a Honda EU2200i run a 10k BTU window AC?

It matches Honda's 2,200 W start and 1,500 W running load, because the EU2200i is 1,800 W rated and 2,200 W maximum. It does not cover Champion's upper start of 2,400 W.

How many watts does a 5k BTU window AC use?

Champion lists 450–600 running watts and 900–1,200 starting watts.

Which figure do I use when the charts disagree?

Use 1,500 W running and 2,400 W starting so one generator covers both published rows.

Can I run the microwave while the compressor starts?

Only if the generator still covers the higher of the two starts on top of the other load's running watts. A 1,000 W microwave is 1,500 W at start and run, which is its own load, not a reason to ignore the air conditioner start.