What Size Generator for a Sump Pump?
A 2,200W inverter handles a 1/2 HP sump pump: 1,050 running watts, 2,150 at start, which fits inside the 2,200W inverter class's 2,200W peak. A 1/3 HP pump is lighter still. The reason to size bigger is everything else that needs power during the same storm.
Wattage by type
| Sump pump type | Running | Starting |
|---|---|---|
| 1/3 HP | 800 W | 1,300 W |
| 1/2 HP (planning number) | 1,050 W | 2,150 W |
| 3/4 HP | 1,400 W | 3,000 W |
| 1 HP | 1,600 W | 3,500 W |
| Battery backup pump (charging) | 150 W | 300 W |
What it takes with company
Same engine as the wattage picker: running total plus the single biggest start spike, then the smallest class that carries it with 20% headroom.
| Load list | Running | Peak | Buy |
|---|---|---|---|
| Sump alone (1/2 HP) | 1,050 W | 2,150 W | 2,200W inverter |
| Sump + fridge | 1,750 W | 3,250 W | 3,400W inverter |
| Sump + fridge + furnace + the basics | 2,750 W | 4,300 W | 3,500W portable |
| Twin sumps in a wet spring + the basics | 2,300 W | 3,400 W | 3,500W portable |
The details that change the answer
Sump pumps fail the storm test in a specific way: the outage and the water arrive together. So while the pump alone runs on a 2,200W inverter, sizing to the pump alone plans for a storm where nothing else in the house matters. The realistic list is pump, fridge, furnace blower, and lights, and that list is a 5,000W portable. The combo table above shows the steps.
One wrinkle unique to sumps: duty cycle. In a hard rain a pump can start every 90 seconds, and every start is the full 2,150W spike. Generators tolerate this fine if the peak fits inside their rating with margin; if the peak barely fits, each start sags the voltage, everything else on the cord blinks, and the pump motor runs hot. This is the one appliance where I'd treat our bare minimum row as genuinely too small.
If both pumps in a two-pump pit can run at once (spring melt, week of rain), count both full spikes. Simultaneous starts are exactly what a flooding basement produces.
Questions people ask
Will a 2,000W generator run a sump pump?
A 1/3 HP pump yes, comfortably: 800 running, 1,300 start. A 1/2 HP pump technically fits (2,150W start against a 2,200W peak rating) but with a 50W margin and nothing else plugged in; every start will sag the line. For a 1/2 HP pump treat 3,400W as the honest floor, and add the fridge math from the table before buying.
Generator or battery backup for the sump?
Different jobs. The battery backup pump covers the 20 minutes to 8 hours you are not home or asleep; the generator covers day two. A $200 battery pump that buys you time to wake up, plus a portable that takes over from there, beats either alone. If the basement floods badly enough to matter, own both.