GenSize generator sizing

What size generator runs a well pump?

Pre-computed outage scenario using the same GenSize formula.

Formula

Running watts + largest startup delta, then 25% headroom.

2.2k4.5k7.5-8.5k9.5-12.5k

Use the 7,500 to 8,500 W portable class as the starting estimate for Well pump, 1 HP.

Running 2,000 W + largest start delta 4,000 W = 6,000 W peak. Add 25% headroom: 7,500 W.

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

Loads used

LoadRunning WStarting WNote
Well pump, 1 HP20006000estimated 3x motor start; verify nameplate and voltage

Models in this class

Westinghouse WGen7500

7,500 running / 9,500 starting W. gasoline.

official Westinghouse page lists 7500 running watts and 9500 peak watts

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Generac GP8000E

8,000 running / 10,000 starting W. gasoline.

official Generac page lists 8000 running watts and 10000 starting watts

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Champion 201281

7,500 running / 9,375 starting W. dual fuel.

current Champion 7500 W dual-fuel model used as successor-class substitute for 100891

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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.