What Size Generator Do I Need for My Well Pump?
Many East County properties rely on private wells for water. During power outages, no electricity means no water. This guide helps you size a generator to power your well pump plus home electrical loads.
Why Well Pumps Require Careful Sizing
Well pumps have extremely high starting surges—often 3x their running wattage. An undersized generator can't handle the startup, causing the generator to overload and shut down. Proper sizing is critical for reliable well water during PSPS events.
Well Pump Wattage by Horsepower
Use this chart to find your well pump's wattage requirements. Check your pump's data plate for exact horsepower rating.
| Pump HP | Running Watts | Starting Watts | Min Generator Size |
|---|---|---|---|
| 1/3 HP | 700 | 1,400 | 3 kW (pump only) |
| 1/2 HP | 1,000 | 2,100 | 4 kW (pump only) |
| 3/4 HP | 1,500 | 3,000 | 5 kW (pump only) |
| 1 HP | 2,000 | 4,000 | 7 kW (pump only) |
| 1.5 HP | 2,500 | 5,000 | 8 kW (pump only) |
| 2 HP | 3,000 | 6,000 | 10 kW (pump only) |
| 3 HP | 4,000 | 8,000 | 13 kW (pump only) |
| 5 HP | 6,000 | 12,000 | 18 kW (pump only) |
Submersible vs Jet Pumps
The two main types of well pumps have slightly different electrical characteristics:
Submersible Pumps
- • Located deep in the well
- • More common in East County
- • Higher starting surge (3-4x running)
- • Typically 1-5 HP for residential
- • Best candidate for soft-start controllers
Jet Pumps
- • Located above ground
- • For shallow wells (under 25 feet)
- • Lower starting surge (2-3x running)
- • Typically 1/2-1 HP for residential
- • Easier to access for maintenance
Soft-Start Controllers: Reduce Surge by 70%
Soft-start controllers are devices installed on well pump motors that dramatically reduce starting surge. This allows smaller generators to power larger pumps:
Soft-Start Benefits
- • Reduces starting surge by 50-70%
- • Extends pump motor life
- • Allows use of smaller generator
- • One-time $300-$600 investment
- • Professional installation recommended
Example with 2 HP Pump:
Without soft-start: 6,000 watt starting surge requires 10+ kW generator
With soft-start: 2,400 watt starting surge allows 5-7 kW generator
Complete Home Sizing with Well Pump
When sizing a generator for a home with a well pump, you need to account for the pump plus all other electrical loads. Here's a complete calculation example:
Example: 2,500 sq ft Home with 1 HP Well Pump
Running Loads:
- • 1 HP well pump: 2,000 watts
- • 3-ton central AC: 3,500 watts
- • Refrigerator: 200 watts
- • Lights/electronics: 1,000 watts
- • Furnace fan: 500 watts
Total Running: 7,200 watts
Highest Starting Surge: AC at 7,000 watts
Calculation: 7,200 + 7,000 = 14,200 watts
Plus 20% buffer: 14,200 × 1.2 = 17,000 watts
Recommended: 18-22 kW Generator
For complete sizing guidance, see our generator sizing guide. For specialized well pump solutions, visit our well pump generator service page.
East County Well Pump Considerations
Properties in Julian, Ramona, Alpine, and backcountry areas often have unique well configurations:
- •Deep wells (300+ feet): Require larger pumps (2-5 HP) with higher starting surge
- •Booster pumps: Some properties have both well pump and pressure booster—account for both
- •Agricultural wells: Larger pumps for irrigation may require commercial-sized generators
- •Storage tanks: If you have a large storage tank, pump runs less frequently but still needs power for refilling
Get Well Pump Generator Sizing Help
Every well system is different. Our free on-site assessment evaluates your well pump specifications, electrical loads, and backup power needs to recommend the right generator size for your East County property.