When the power goes out and you're on a private well, you lose water too. Here's the complete 2025 guide to sizing a generator for your well pump — with real wattage numbers for every common pump size.
Homeowners on city water don't have to worry about this — but if your home draws from a private well, a power outage means no water for drinking, bathing, or flushing toilets. Well pumps are motor loads with significant starting surges, and they're often the largest motor load in a rural home's backup power plan. Getting the generator size right here is critical.
💡 Combine your well pump with all other loads: Use our free generator size calculator to build a complete load list and get a precise generator recommendation.
Well pumps come in two main types — shallow well (jet pumps for wells under 25 feet) and deep well (submersible pumps for wells from 25 to 400+ feet). Both have similar wattage patterns but submersible pumps tend to be larger HP and higher voltage.
| Pump Type / HP | Voltage | Running Watts | Starting Watts | Min. Generator |
|---|---|---|---|---|
| Shallow jet pump, 1/3 HP | 120V | 600–750 W | 1,400–1,800 W | 2,500 W |
| Shallow jet pump, 1/2 HP | 120/240V | 750–1,000 W | 2,000–2,500 W | 3,500 W |
| Deep well submersible, 1/2 HP | 240V | 800–1,000 W | 2,000–2,500 W | 3,500 W |
| Deep well submersible, 3/4 HP | 240V | 1,000–1,500 W | 2,500–3,000 W | 5,000 W |
| Deep well submersible, 1 HP | 240V | 1,500–2,000 W | 3,500–5,000 W | 6,500 W |
| Deep well submersible, 1.5 HP | 240V | 2,000–2,500 W | 5,000–6,000 W | 7,500 W |
Find your pump's HP: The horsepower and voltage are printed on the motor nameplate. Submersible well pumps are typically 240V and require a generator with a 240V / 30A outlet (L14-30 or L6-30 receptacle) and a properly wired transfer switch.
Most deep well submersible pumps run on 240 volts, not the 120V that most appliances use. This has important generator implications:
For help with the transfer switch side, consult a licensed electrician. The generator sizing math is what we cover here; safe electrical installation is a separate (and legally required) step.
If you only care about keeping water flowing and nothing else, a 3,500W generator with a 4,375W surge rating handles a 1/2 HP well pump safely. Keep in mind you'd have very little headroom for other loads while the pump runs.
Well pump (1/2 HP): 900W running / 2,500W starting
Refrigerator: 175W running / 1,200W starting
Lights + chargers: 250W running
Total running: 900 + 175 + 250 = 1,325W running.
Peak (well pump starting, largest surge): 1,325 + 2,500 = 3,825W peak.
A 5,000W generator (typically 6,250W surge) handles this with solid headroom. Most rural homeowners land here.
A deeper well with a 3/4 HP pump needs 3,000W starting. Add refrigerator, lights, a window AC, and the furnace fan and you're looking at:
Running: 1,400 + 175 + 1,100 + 700 + 250 = 3,625W running.
Peak (well pump surge): 3,625 + 3,000 = 6,625W peak.
A 7,500W generator (9,375W surge) handles this confidently. This is the right size for most rural properties with a 3/4 HP well pump.
Must have a 240V twist-lock outlet (L14-30). Pair with a manual transfer switch for the well pump circuit. Dual-fuel models extend runtime during rural outages when fuel resupply may be difficult.
→ Browse 5,000W Generators with 240V Outlet on Amazon
A 7,500W generator with 9,375W surge handles large well pumps plus a full complement of home essentials. Dual-fuel is essential for rural properties — propane stores safely for years without fuel stabilizer.
→ Browse 7,500W Dual-Fuel Generators on Amazon
Properties with multiple water circuits, larger pumps, barn equipment, or outbuildings need 10,000W+ for comfortable backup. Standby generators running on a propane tank are the most practical long-term solution for rural properties that experience frequent extended outages.
For a 1/2 HP well pump, a 3,500W generator (4,375W surge) is the minimum; a 5,000W generator is recommended if you're also running a refrigerator and lights. For a 3/4 HP pump, a 5,000–7,500W generator is the right range. Always check the pump's starting wattage, not just running wattage.
Yes — for a 1/2 HP pump (2,500W starting), a 3,500W generator (4,375W surge) works but has limited headroom for other loads at the moment the pump starts. If the refrigerator's compressor happens to kick on at the same time the well pump starts, you may trip the generator's overload. A 5,000W generator provides a comfortable safety margin.
Yes — especially for 240V well pumps. A transfer switch or interlock kit is required to safely connect a generator to your home's electrical panel. For 240V pump circuits, you cannot use extension cords safely. A licensed electrician can install a manual transfer switch that includes the well pump circuit for $400–$900.
A typical residential pressure tank (20–44 gallons) pressurizes in 1–3 minutes of pump run time once the pressure switch triggers. During normal use, the well pump may cycle on for 1–3 minutes every 30–60 minutes. You don't need to run the generator continuously — cycle it on when the pressure drops, pressurize the tank, then shut it off to conserve fuel.
Free tool — check off all your loads for an exact recommendation.
Running and starting watts for pumps, HVAC, and 40+ appliances.
Sump pump generator sizing — smaller HP but same starting surge math.
Full home load breakdown including well pump, AC, fridge, and more.