What Size Generator Do You Need for a Well Pump?
Without power, a well pump means no running water and no flushing toilets. Most well pumps run on 240 volts and have a big starting surge, so they rule out small inverter generators and need a portable with a 240-volt outlet, or a standby unit.
| Appliance | Running / starting W | On its own | With fridge, lights and Wi-Fi |
|---|---|---|---|
| Well pump (1/2 HP) | 1,000 / 2,100 | 5,000-watt 10 kW standby | 5,000-watt 10 kW standby |
| Well pump (3/4 HP) | 1,500 / 3,000 | 5,000-watt 10 kW standby | 5,000-watt 10 kW standby |
| Well pump (1 HP) | 2,000 / 5,000 | 5,000-watt 10 kW standby | 6,500-watt 10 kW standby |
Smallest portable (by starting watts) and smallest standby generator on natural gas, keeping about 20% headroom.
Tips
- Check the pump's horsepower on its control box or the well report; deep-well pumps are often 1 HP or more.
- A three-wire pump with a separate control box usually starts more gently than a two-wire pump of the same size.
- Plan for the pump to start while the fridge and other loads are already running: that's the moment that decides the size.
See also the appliance wattage chart and what each generator size can run.