What Size Generator Do I Need to Run a Well Pump?

Horsepower changes the start by a wide margin. Read the row that matches the pump.

Longer size guide: which generator size fits a well pump.

Quick answer: Champion lists a 1/2 hp well pump at 750–1,000 running watts and 1,500–2,000 starting watts, and a 1 hp well pump at 1,000–2,000 running watts and 2,000–4,000 starting watts. Covering the 1 hp row takes a running rating that clears 2,000 W and a starting rating that clears 4,000 W. A single Honda EU2200i, rated 1,800 W with a 2,200 W maximum, covers the 1/2 hp row but not the 1 hp row, while two EU2200i units in parallel reach up to 4,400 W and the Champion manual lists 5,000 W running and 6,250 W starting.

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Running and starting watts

Load	Running watts	Starting watts	Source
Well pump, 1/2 hp	750–1,000	1,500–2,000	Champion
Well pump, 1 hp	1,000–2,000	2,000–4,000	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.

Honda's wattage guide does not list a well pump, so this page does not borrow one. A hardwired pump needs a transfer switch or interlock installed by an electrician. See the transfer switch sizing guide.

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 size generator for a 1/2 hp well pump?

Champion lists 750–1,000 W running and 1,500–2,000 W starting. The EU2200i rated output is 1,800 W and the maximum is 2,200 W, which covers that row.

What size generator for a 1 hp well pump?

Clear 2,000 W running and 4,000 W starting. Parallel EU2200i output is up to 4,400 W. The manual lists 5,000 W running and 6,250 W starting.

Does a single EU2200i cover a 1 hp pump?

No. The pump can draw 2,000 W running, above the 1,800 W rated output, and 4,000 W starting, above the 2,200 W maximum.

Where is the longer well-pump writeup?

Linked at the top. This page only answers the sizing question from Champion's 1/2 hp and 1 hp rows.