What Size Generator Do You Need for a Sump Pump?
A sump pump is often the main reason people buy a generator: when a storm knocks the power out, the basement is filling at the same time. Most pumps draw under 1,100 running watts but need about twice that to start, every time the float switch kicks on.
| Appliance | Running / starting W | On its own | With fridge, lights and Wi-Fi |
|---|---|---|---|
| Sump pump (1/3 HP) | 800 / 1,300 | 2,000-watt 10 kW standby | 3,000-watt 10 kW standby |
| Sump pump (1/2 HP) | 1,050 / 2,150 | 3,000-watt 10 kW standby | 3,000-watt 10 kW standby |
Smallest portable (by starting watts) and smallest standby generator on natural gas, keeping about 20% headroom.
Tips
- Run the pump on a dedicated circuit or cord so a tripped breaker elsewhere can't stop it.
- Add a battery backup pump as a second line of defense; it covers the minutes before you start a portable generator.
- If you're often away during storms, consider an automatic standby generator: a portable only helps if someone is home to start it.
See also the appliance wattage chart and what each generator size can run.