What Size Generator for Well Pump?
Well pumps are challenging because of their high startup surge - typically 3x running watts. Most residential well pumps need a generator with at least 3000W surge capacity.
Minimum Size
3000W
bare minimum, tight
Comfortable Size
4000W
recommended
Ideal Size
5000W
room to grow
Total Running Watts
750W
Total Surge/Starting Watts
2250W
Generator Sizing Calculator
Additional Custom Load
Running Watts
3750W
Surge Watts
11250W
Recommended Generator
14500W+
Includes 25% headroom for reliable operation
Suitable Generator Sizes
Estimated Fuel Usage
* Fuel estimates are approximate. Actual consumption varies by generator model, load, and altitude.
Typical Loads for Well Pump
| Item | Running Watts | Surge Watts |
|---|---|---|
| 1/2 HP Submersible | 500W | 1500W |
| 3/4 HP Submersible | 750W | 2250W |
| 1 HP Submersible | 1000W | 3000W |
| 1.5 HP Submersible | 1500W | 4500W |
| Total | 750W | 2250W |
* Surge watts apply to motor loads during startup. Size your generator for worst-case surge scenario.
Generator Sizing Tips
- •Know your pump horsepower before sizing a generator
- •A soft-start capacitor can reduce surge by 50-70%
- •Run water into a storage tank to reduce pump cycling
- •Never run the pump dry - this destroys the motor
- •Deep well pumps require more power than shallow well jets
Key Considerations
- ⚠Water pressure tank size affects how often pump cycles
- ⚠Generator must be sized for surge, not running watts
- ⚠Store water during outage to reduce pump runtime
Alternatives to Consider
- ✓Soft-start capacitor to reduce surge
- ✓Water storage tank to reduce pump cycles
- ✓Hand pump for backup
Frequently Asked Questions
What size generator for a well pump?
For a 1/2 HP pump, minimum 2000W generator (3000W preferred). For 1 HP, minimum 3500W (4000W+ preferred). The startup surge is 3x running watts, so size for surge, not running.
Can a 3000W generator run a well pump?
For pumps up to 3/4 HP, yes. A 1 HP pump has 3000W surge which is right at the limit. For reliability, size up to 4000W or add a soft-start to the pump.
Why does my generator struggle to start the well pump?
The startup surge exceeds your generator capacity. Solutions: larger generator, soft-start capacitor on the pump, or make sure no other loads are on when starting the pump.