What Size Generator Do I Need to Run an Air Compressor?

The one-horsepower start is the planning figure. Larger compressors on the same chart jump past it.

Quick answer: Honda lists a 1 hp air compressor at 1,600 running watts and 4,500 starting watts, and Champion lists a 1 hp compressor at 1,500 running watts and 4,500 starting watts. Covering both takes a running rating that clears 1,600 W and a starting rating that clears 4,500 W. Two Honda EU2200i units in parallel reach only up to 4,400 W, short of that start, while the Champion manual lists 6,250 W starting.

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Running and starting watts

Load	Running watts	Starting watts	Source
Air compressor, 1/2 hp	975	1,600	Honda
Air compressor, 1 hp	1,600	4,500	Honda
Air compressor, 1 hp	1,500	4,500	Champion
Air compressor, 2 hp	2,500	7,500	Champion
Air compressor, 3 hp	3,500	10,500	Champion

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 1/2 hp compressor is a different row: Honda lists 975 running watts and 1,600 starting watts, which fits the EU2200i rated output of 1,800 W and maximum of 2,200 W. Larger Champion rows do not fit the manual's starting rating: 2 hp is 2,500 W running and 7,500 W starting, and 3 hp is 3,500 W running and 10,500 W starting, both above 6,250 W starting.

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

What starting watts does a 1 hp air compressor need?

Both charts list 4,500 starting watts. Honda lists 1,600 W running and Champion lists 1,500 W running.

Can parallel EU2200i units start a 1 hp compressor?

Parallel output is up to 4,400 W. The start is 4,500 W, so they are short.

What about a 1/2 hp compressor?

Honda lists 975 W running and 1,600 W starting. That fits an EU2200i at 1,800 W rated and 2,200 W maximum.

Do 2 hp and 3 hp compressors fit a 6,250 W start?

No. Champion lists 7,500 W starting for 2 hp and 10,500 W starting for 3 hp. The manual lists 6,250 W starting.