Quick answer
If you want one machine to keep a household sump pump and a few essentials running through an outage, buy an inverter generator with a CO shutoff and surge watts well above your pump's label, such as the WEN DF360iX 3600-Watt Dual Fuel Inverter Generator, rated 4.4 stars across 531 Amazon ratings. Its listing gives 2,900 rated and 3,600 surge watts on gasoline. Size it yourself: volts times amps on the pump label gives running watts, and the start-up surge runs several times higher. Run it outdoors, well away from windows and doors, and plug the pump in with a heavy-duty outdoor cord. Never backfeed a wall outlet.
Buyer's Guide
What to know before you buy.
Size the Generator From Your Pump's Label
Start with the label on the pump or its manual, not a horsepower chart. Multiply volts by amps to get running watts: a pump marked 9.5 amps at 115 volts draws about 1,090 watts while it runs. Motors also pull a short surge to start, often several times the running draw, and that surge is what stalls an undersized generator. Some manuals list a starting figure. If yours does not, compare the generator's surge or peak rating with a generous margin over the running watts. Then add whatever else will share the generator, such as a refrigerator, a freezer, a few lights and a phone charger. Total their running watts, and remember that two motors starting together add their surges. Buy a generator whose rated watts, not its peak watts, cover that total.
Inverter or Conventional: What a Pump Actually Needs
An inverter generator turns the engine's output into steady, clean power, and many models throttle the engine down when the load is light. A sump pump motor does not need clean power. What an inverter gives a pump owner is quiet and fuel economy, because a pump that runs in short bursts leaves the generator lightly loaded for most of the night. A conventional open-frame generator holds its engine at full speed, so at the same light load it burns more fuel and makes more noise, but it usually gives more watts for the money. Both work. Pick an inverter if neighbors are close or fuel runs are hard, and a conventional unit like the Westinghouse 4650 for surge on a budget. Small camping inverters need a careful check of their surge figure against your pump.
Run Time, Fuel and Storage
Listings that state run time usually give it at 25% load, and a storm night with a busy pump can sit above that. The Westinghouse iGen12000DFc gives the clearest figure here: up to 19 hours at 25% load on a 7.9 gallon tank. Neither WEN listing gives a run time, so find it in the manual. Gasoline is the weak link in storm prep. It degrades in storage within months unless you treat it with stabilizer, and stale fuel gums up carburetors, which is why a fuel shutoff for draining the carburetor before storage is worth having. Propane keeps in a sealed cylinder, so a dual-fuel generator with two full tanks in the shed is ready whenever the power drops. Store fuel outside the living space, away from the water heater and furnace, in approved containers.
Cords, Transfer Switches and Backfeeding
There are two safe ways to connect. The simple one is to plug the pump straight into the generator with a heavy-duty, outdoor-rated, three-prong extension cord sized for the pump's amps and long enough to keep the generator well away from the house. The better one is a manual transfer switch or interlock kit, installed by a licensed electrician, so the generator feeds chosen circuits through the panel. Never connect a generator to a wall outlet or dryer receptacle with a double-ended cord. That is backfeeding, and electrical codes prohibit it: it can send power back up the utility lines and injure line workers, and it can start a fire in your own wiring when the grid comes back. Keep spare cord out of puddles and every plug connection off wet ground.
Carbon Monoxide: Where the Generator Goes
Generator exhaust carries carbon monoxide, which you cannot see or smell, and it kills people every storm season. Run the generator outdoors only, never in a garage, basement, crawl space or enclosed porch, even with the doors open. Keep it well away from doors, windows and vents, with the exhaust pointing away from the house, and follow the minimum distance in its manual. Every generator on this page lists a CO shutdown sensor, which turns the engine off if CO builds up around the machine; it does nothing for the people indoors. For them, fit CO alarms on every level of the house and outside sleeping areas, with battery power or battery backup. Keep the generator dry in rain under a cover made for running generators, never under a closed tarp.
Who Should Not Buy a Generator for the Sump Pump
A generator only helps if someone is home to start it, fuel it and move it. If you travel, work long shifts or cannot roll a heavy machine outside in a storm, a battery backup sump pump is the better first buy, because it switches on by itself when the main pump loses power. A generator also does nothing for a burned-out pump, a stuck float or a frozen discharge line, so a high-water alarm earns its place either way. Condo owners and renters usually cannot run a generator safely outdoors or have a transfer switch fitted. If water gets in anyway, EPA advises drying water-damaged areas within 24 to 48 hours to prevent mold. And if the basement floods with the pump running, the fix is pump capacity or drainage, which is a job for a plumber, not more watts.
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