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

Size the start from both charts, then see whether one small inverter's maximum covers it.

Quick answer: Honda lists a 1/2 hp sump pump at 1,050 running watts and 2,150 starting watts, and Champion lists the same size at 800–1,050 running watts and 1,300–2,150 starting watts. Covering both takes a running rating that clears 1,050 W and a starting rating that clears 2,150 W. A Honda EU2200i is rated 1,800 W with a 2,200 W maximum, which covers that 1/2 hp start.

Affiliate

Affiliate disclosure: as an Amazon Associate, we earn from qualifying purchases — at no cost to you.

Shop generators this size on Amazon

Running and starting watts

Load	Running watts	Starting watts	Source
Sump pump, 1/3 hp	800	1,300	Honda
Sump pump, 1/2 hp	1,050	2,150	Honda
Sump pump, 1/3 hp	500–800	1,000–1,600	Champion
Sump pump, 1/2 hp	800–1,050	1,300–2,150	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 1/3 hp pump is lighter. Honda lists 800 running watts and 1,300 starting watts. Champion lists 500–800 running watts and 1,000–1,600 starting watts. If a fridge is also on the generator, add the fridge's running watts and keep only the higher start.

Check a full load list on the generator size calculator.

Affiliate

Shop generators this size on Amazon Heavy-duty generator extension cords on Amazon

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

FAQ

What size generator for a 1/2 hp sump pump?

Clear 1,050 W running and 2,150 W starting. The EU2200i maximum is 2,200 W and the rated output is 1,800 W.

What about a 1/3 hp sump pump?

Honda lists 800 W running and 1,300 W starting. Champion lists 500–800 W running and 1,000–1,600 W starting.

Do Honda and Champion agree on the 1/2 hp start?

The top of both ranges is 2,150 W. Champion's full start range is 1,300–2,150 W, and the running range is 800–1,050 W.

Is this the whole sump guide?

No. This page is the sizing question only. The longer wattage guide is linked at the top. The 1/2 hp start to cover is still 2,150 W.