Before you buy a generator for your well, you need to know one thing that many homeowners never learned: what kind of pump you actually have. A jet pump and a submersible pump both move water from your well to your house, but they sit in different places, can run on different voltages, and behave differently when you put them on generator power. Guess wrong and you can end up with a generator that will not start the pump, or one that is far bigger than you need.
This guide shows you how to tell which pump you have, compares their wattage requirements side by side, and explains what size generator each one really needs.
How to Tell Which Pump You Have
A jet pump sits above ground. You will usually find it in a basement, well house, or pump house. It looks like an electric motor attached to a snail-shaped metal housing, with pipes running to the well and to the pressure tank. A shallow-well jet pump has one pipe running down into the well. A deep-well jet pump has two.
A submersible pump sits down in the well, under the water. At the surface you will see a sealed well cap with a conduit or cable going in and a single pipe leading to your house. There is no motor sitting next to your pressure tank, though you may see a small control box nearby if you have a 3-wire pump.
If you are still unsure, check the pump’s nameplate or your well installation paperwork, or look at the breaker for the pump circuit. A well professional can also identify it quickly.
How Each Pump Draws Power
Both types use an electric motor, and both draw a burst of extra power at startup, often two to three times their running watts. In that sense they behave alike. At the same horsepower, their running and starting watts fall in a similar range, which is why horsepower matters more than pump type when you size a generator.
The differences show up in efficiency and voltage. Jet pumps are generally less efficient than submersibles, particularly for deeper wells, because they use some of the water they pump to create suction. Submersibles push water up from below and tend to use energy more directly. For shallow wells that difference matters less.
Wattage Chart: Jet Pump vs. Submersible Pump
These are approximate planning figures. Always check your own nameplate, because brands and ages vary.
| Horsepower | Jet Pump Running | Jet Pump Starting | Submersible Running | Submersible Starting |
|---|---|---|---|---|
| 1/2 HP | 900 – 1,100 W | 1,800 – 2,400 W | 1,000 – 1,100 W | 2,000 – 2,500 W |
| 3/4 HP | 1,300 – 1,500 W | 2,600 – 3,200 W | 1,400 – 1,600 W | 3,000 – 3,500 W |
| 1 HP | 1,700 – 2,000 W | 3,400 – 4,200 W | 1,800 – 2,000 W | 3,500 – 4,500 W |
The takeaway is simple: size by horsepower and by the nameplate amps and volts, not by the type of pump. A 3/4 HP jet pump and a 3/4 HP submersible need generators in the same general class.
Voltage Matters as Much as Watts
Voltage is where the two pump types most often differ, and it directly affects which generator outlet you need.
- Submersible pumps are most commonly 240 volts, though smaller models can be 120 volts.
- Jet pumps are often dual-voltage, meaning they can be wired for either 115 or 230 volts. At the lower voltage the pump draws about twice the amps for the same power, so the wiring and breaker differ.
Check the nameplate for the voltage and look at how your pump is actually wired. A 240-volt pump needs a generator with a 240-volt outlet and a safe connection method. A 120-volt pump can run from a standard generator outlet, but make sure the extension cord or transfer switch circuit can handle the amperage.
2-Wire vs. 3-Wire Submersible Pumps
Submersible pumps come in two wiring styles, and the difference affects troubleshooting more than generator sizing.
- 2-wire pumps have their starting components built into the motor down in the well. There is no control box.
- 3-wire pumps have their start capacitor and relay in a control box mounted at the surface, usually near the pressure tank.
A failing capacitor or relay in a 3-wire control box can cause excessive current draw and repeated generator trips, even when the generator is properly sized. If a correctly sized generator keeps tripping, see our guide on well pumps tripping the generator breaker.
What Size Generator Does Each Pump Need?
These guidelines add the pump to a refrigerator and a few lights. Add more capacity for any other large loads. Our guide on how many watts you need to power a rural home shows how to total everything.
| Pump Size | Suggested Generator (Running / Peak) |
|---|---|
| 1/2 HP (jet or submersible) | 3,500 – 4,500 W running, about 4,500+ W peak |
| 3/4 HP | 5,000+ W running, about 6,500 W peak |
| 1 HP | 7,500+ W running, about 9,000 W peak |
Jet Pump Quirks to Know About on Generator Power
- Priming. A jet pump can lose its prime during an outage, especially if the foot valve leaks. If you get power back and the pump runs but delivers no water, see our guide to repriming a well pump after an extended outage.
- Dual-voltage wiring. If your jet pump is wired for 115 volts and you move to a 240-volt generator connection, you cannot just plug it in. The wiring and breaker must match.
- Visible and serviceable. Because it sits above ground, a jet pump is easier to inspect and test with a clamp meter than a submersible.
Submersible Pump Quirks to Know About on Generator Power
- Hardwired, 240 volts. Most are connected directly to a double-pole breaker, so a transfer switch or interlock kit is the safe way to power them.
- Hidden problems. Because the pump is down the well, symptoms like low water, tripping, or humming require more detective work. Start with the breaker, pressure switch, and control box. See well pump won’t restart after the power comes back.
- Long cable runs. Deep wells use long cables with some voltage drop. If your pump struggles on generator power but not on grid power, that can be a factor.
Can a Power Station Run Either One?
Most small and mid-size power stations cannot run a 240-volt pump because they lack the voltage and surge capacity. A few large units can. The EcoFlow DELTA Pro 3, for instance, is listed with 4,000 watts of output, 120/240-volt support, and suitability for loads like a 1 HP water pump. A smaller 120-volt jet pump might also work on a large power station if the inverter can handle the surge, but check the specifications carefully. For a deeper look, read our guide on how many solar panels you need to run a well pump.
Recommended Products
To find out what your pump really draws, a Klein Tools CL800 digital clamp meter lets you read running amps at the pump’s supply wire and compare them with the nameplate. Only use a clamp meter if you are comfortable working safely around live electrical equipment, and consider hiring an electrician or well technician instead. #CommissionsEarned
For a 1/2 HP pump with a smaller generator budget, the WEN DF475T, a 4,750-watt peak dual-fuel unit with 120/240-volt outlets, can handle the pump when you stagger other loads. For more headroom with a 3/4 HP pump, the Westinghouse WGen5300DFcv offers 5,300 running and 6,500 peak watts. #CommissionsEarned
For a 1 HP pump with other household loads, the Champion 100165 provides 7,500 running and 9,375 starting watts on gasoline, which gives you a more comfortable margin. See our guide on running a well pump and sump pump together for combined examples. #CommissionsEarned
To connect any of these safely, a Reliance Controls Pro/Tran 2 306CRK transfer switch provides a double-pole 240-volt position suited to a well pump circuit, plus several 120-volt circuits, and should be installed by a licensed electrician. See our transfer switch guide for well pumps. #CommissionsEarned
Common Mistakes to Avoid
Assuming pump type determines generator size. Horsepower, voltage, and nameplate amps matter more.
Ignoring voltage. A 240-volt pump cannot run from a 120-volt outlet, and a dual-voltage jet pump must be wired correctly for the supply you use.
Sizing for running watts only. Include the startup surge.
Skipping the transfer switch. Do not backfeed a generator through a wall outlet.
Not preparing for priming problems. A jet pump may need repriming after an outage.
FAQ
Do jet pumps use more power than submersible pumps?
At the same horsepower, running and starting watts are similar. Jet pumps can be less efficient for deeper wells, which means they may use more energy to deliver the same water.
How do I know if my well pump is 120V or 240V?
Check the nameplate on the pump or control box, and look at the breaker. A double-pole breaker usually indicates 240 volts.
What size generator do I need for a 1/2 HP well pump?
Roughly 3,500 to 4,500 running watts with a peak rating around 4,500 or more, including a refrigerator and lights.
Can I plug a well pump into a generator?
Rarely. Most are hardwired. Use a transfer switch or interlock kit installed by a licensed electrician.
Do both pump types need priming?
Jet pumps may need repriming after an outage. Submersibles sit in the water and generally do not.
Which is easier to troubleshoot?
A jet pump, because it is above ground and accessible. A submersible is harder to inspect without a well technician.
This article is general information, not electrical or plumbing advice. Consult a licensed professional for electrical work.
Disclosure: This post contains affiliate links. As an Amazon Associate, we earn from qualifying purchases at no additional cost to you.