What size generator runs a sump pump?

Use the about 4,500 W inverter class as the starting estimate for Sump pump, 1/3 HP.

Running 800 W + largest start delta 1,600 W = 2,400 W peak. Add 25% headroom: 3,000 W.

Sizing estimate only - confirm with a licensed electrician; never backfeed a panel.

Loads used

Load	Running W	Starting W	Note
Sump pump, 1/3 HP	800	2400	estimated 3x motor start

Models in this class

Westinghouse iGen4500

3,700 running / 4,500 starting W. gasoline.

official manual lists 3700 running watts and 4500 peak watts

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Champion 100302

3,500 running / 4,000 starting W. gasoline.

official manual lists model 100302 with 3500 running watts and 4000 starting watts

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Generac GP3600

3,600 running / 4,500 starting W. gasoline.

official Generac page lists 3600 running watts and 4500 starting watts

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Why the estimate can change

Use nameplate watts when available. Pumps, compressors, altitude, fuel type, and extension-cord voltage drop can all change the practical generator size.