As an Amazon Associate I earn from qualifying purchases. Links to Amazon on this page are affiliate links.
What size generator do you need for a sump pump?
Updated
Using the typical figure in our calculator, a 1/2 HP sump pump needs about 1,000 running watts and 2,100 starting watts. With headroom, look for at least 1,250 running watts. Add a refrigerator and you need 1,700 running and 3,200 starting watts, so look for about 2,150 running watts.
The math
| What you run | Running watts | Starting watts | Look for at least |
|---|---|---|---|
| One 1/2 HP sump pump | 1,000 | 2,100 | 1,250 running |
| Sump pump and refrigerator | 1,700 | 3,200 | 2,150 running |
| Two 1/2 HP sump pumps | 2,000 | 3,100 | 2,500 running |
Starting watts here means all running watts plus the single largest starting burst. That is how the wattage calculator works, because motors rarely start at the same moment. Two sump pumps in the same pit can be the exception. If both could kick on together in a fast-rising pit, plan for both bursts: 4,200 starting watts.
Pumps come in other sizes too. Check the label on your pump for watts, or multiply volts by amps, and type that number into the calculator.
Which picks fit
- The Champion 4000-Watt Dual Fuel has 3,000 running and 4,000 starting watts on gas. That covers a pump and a refrigerator with room left. It has a CO shutoff and runs on propane, which keeps for years between storms. The caveat: on propane you get 2,700 running watts, and the listing names no electric start.
- The Westinghouse iGen5000DF has 3,900 running watts and electric start. That is handy when you need it going fast in bad weather. The caveat: it weighs about 105 pounds.
- The WEN 56235i covers one pump on paper, with 1,900 running and 2,350 surge watts. We would not lean on it for this job. Owners are mixed on how it holds large loads, and a sump pump is not a load you want to gamble on.
All five picks are compared on the roundup page.
Storm setup
- Most sump pumps plug into a normal outlet. Run a heavy-duty, outdoor-rated extension cord from the generator to the pump. No transfer switch is needed for that.
- Sump pumps run when it rains, and a generator must stay dry. The Red Cross says to run it on a dry surface under an open, canopy-like cover, such as a tarp held up on poles. Not in the garage, and not on the porch.
- Keep the cord connection out of standing water, and do not touch the generator with wet hands.
- Test the whole setup on a dry day. Start the generator, plug in the pump and lift the float.
If your pump is wired straight into the house with no plug, you need a transfer switch or interlock and a licensed electrician.
Safety first, every time
- Carbon monoxide kills. Never run a generator indoors, in a garage, in a shed or on a porch, even with the door open. Keep it at least 20 feet from the house. Point the exhaust away from windows, doors and vents. Put battery CO alarms inside your home.
- Never backfeed. Do not plug a generator into a wall outlet or dryer outlet. It can kill a utility worker or a neighbor and can start a fire. To power home circuits you need a transfer switch or an interlock kit, installed by a licensed electrician.
- Without that, run heavy-duty outdoor extension cords from the generator straight to each appliance.
- Let the engine cool before you refuel. Store fuel outside the house.