Home › Generator Size For Sump Pump
Generator Size For Sump Pump
Quick answer: A generator for a sump pump must cover the pump's running watts plus its brief start surge, often two to three times running, along with anything else you plug in. Enter running watts, a surge multiplier, other loads and headroom. The result gives running and peak watts to compare with a generator's continuous and surge ratings.
Where the numbers come from
Running watts are on the pump label or estimated as amps × 120 V. Induction motors draw a large inrush current for a fraction of a second when starting; multipliers of 2–3× are common planning values, and some pumps list starting watts directly. Other loads might include a fridge, furnace blower or lights. Headroom keeps the generator out of overload.
Worked example
An 800 W pump with a 3× surge, plus 400 W of other loads and 20% headroom: running ≈ 1,440 W, starting peak ≈ 3,360 W. A generator rated at least about 1,500 W continuous and 3,400 W surge would be the planning floor.
Illustrative note (2026-10-29): Values in this example were assumed on 2026-10-29 for illustration only.
Safety
Run generators outdoors, away from windows and doors, because of carbon monoxide. Never backfeed a home through an outlet. Any inlet, interlock or transfer switch must be installed by a licensed electrician to local code.