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What Size Generator to Run a Sump Pump?

Last updated:

Fact-checked by Marcus Hayes, Master Electrician (License #CA-EL-89241), 15 years generator installation experience.

A sump pump is one of the most critical appliances to keep running during a power outage — it protects your basement from flooding. But sump pumps have high starting watt surges that trip undersized generators. This guide helps you calculate the exact generator size for your sump pump.

Key Takeaways

  • A 1/2 HP sump pump needs 1,050 running watts and 3,150 starting watts — you need at least a 3,200W generator.
  • Sump pumps have induction motors with 3x starting watt surges that can trip undersized generators.
  • A solar generator with 2,400W+ surge output can run a sump pump indoors with no emissions.
  • A 4,000Wh battery backup can run a 1/2 HP sump pump for 3-4 hours of continuous operation, or 18-20 hours at typical duty cycles.
  • For multi-day flooding, add a 400W solar panel for daily recharge.

How many watts does a sump pump use?

A 1/3 HP sump pump uses 800 running watts and 2,400 starting watts. A 1/2 HP sump pump uses 1,050 running watts and 3,150 starting watts. A 3/4 HP sump pump uses 1,500 running watts and 4,500 starting watts. The starting watt surge is 3x the running wattage because sump pumps use induction motors that need a large burst of power to start.
Pump Size Running Watts Starting Watts Min. Generator Size
1/3 HP 800W 2,400W 2,500W
1/2 HP 1,050W 3,150W 3,500W
3/4 HP 1,500W 4,500W 5,000W
1 HP 2,000W 6,000W 6,500W

Best generators for sump pump backup

For a gas generator, the Westinghouse iGen5000DFc (5,000W starting) handles any residential sump pump. For a battery backup, the EcoFlow Delta Pro 3 (4,000W output, 8,000W surge) runs a sump pump indoors with no emissions — critical if your sump pump is in a basement where you cannot run a gas generator.

The biggest advantage of a solar generator for sump pump backup is indoor use. Gas generators must be placed outdoors 20 feet from the house, which means running a long extension cord to the basement sump pump. A solar generator sits right next to the sump pump, plugged in directly, with no extension cord and no CO risk. During a storm when flooding is happening, this is a significant advantage.

Frequently Asked Questions

What size generator do I need to run a sump pump?
A typical 1/2 HP sump pump needs 1,050 running watts and 3,150 starting watts. You need a generator with at least 3,200 starting watts to handle the surge. A 3,500W generator like the Westinghouse iGen4500 provides comfortable headroom. For a 1/3 HP sump pump (800W running, 2,400W starting), a 2,500W generator is sufficient.
Can a 2000W generator run a sump pump?
A 2,000W generator can run a 1/3 HP sump pump (2,400W starting) if it has at least 2,400 starting watts. The Honda EU2200i (2,200W starting) is slightly under the requirement for a 1/2 HP pump. For reliable sump pump backup, use a 3,000W+ generator or a solar generator with at least 2,400W surge output.
Can a solar generator run a sump pump?
Yes. A solar generator with at least 2,400W surge output can run a sump pump. The EcoFlow Delta Pro 3 (4,000W output, 8,000W surge) and Anker SOLIX F3800 (6,000W output, 9,000W surge) both handle sump pumps easily. A 4,000Wh unit can run a 1/2 HP sump pump (1,050W) for 3-4 hours of continuous operation, or much longer with intermittent cycling.
How long will a battery backup run a sump pump?
A sump pump cycles on and off based on water level, typically running 10-30% of the time during active flooding. A 2,000Wh solar generator running a 1/050W sump pump at 20% duty cycle lasts about 9-10 hours. A 4,000Wh unit lasts 18-20 hours. For multi-day flooding, add a 400W solar panel for daily recharge.
How many watts does a sump pump use?
A 1/3 HP sump pump uses 800 running watts and 2,400 starting watts. A 1/2 HP sump pump uses 1,050 running watts and 3,150 starting watts. A 3/4 HP sump pump uses 1,500 running watts and 4,500 starting watts. The starting watt surge is 3x the running wattage because sump pumps have induction motors.