Generator for Well Pump: Sizing and Start-Up

Understanding well pump watts

A well pump is a motor-driven appliance that draws water from a well. On a generator listing, the pump's power needs are described by two figures: running watts and starting watts. Running watts are what the pump uses while it is operating steadily. Starting watts, also called surge watts, are the higher draw for the brief moment the motor starts. The starting figure is always larger than the running figure.

When you compare a generator to a well pump, you are comparing two sets of stated figures. The generator listing shows its starting watts and running watts. The pump's nameplate or manual shows its running watts and starting watts. The generator's starting watts must be at least as high as the pump's starting watts, and its running watts must cover the pump's running watts. If the generator's starting watts are lower, the pump may not start.

The first watts figure in a generator title is often the starting figure. Read the listing carefully to see which figure is which. The maker's page for the generator usually lists both figures. The pump's maker can confirm the pump's starting and running watts for the specific model.

• Running watts: the steady draw while the pump operates.
• Starting watts: the brief surge when the motor starts.
• Generator starting watts must meet or exceed pump starting watts.
• Generator running watts must meet or exceed pump running watts.

Reading the generator listing

Generator listings on this site state the starting and running watts in the title or in the bullet list. The title often names one figure, usually the starting watts. For example, a title like "7,500-Watt Generator" typically refers to starting watts. The running watts figure appears in the details or on the maker's page.

When you see a watts figure in a title, check whether the listing says "starting watts" or "running watts." If the listing does not specify, the maker's page will. The catalogue groups generators by starting watts, so the guides on this site use the first figure as the starting figure. See how to read a generator listing for more.

For a well pump, the starting watts are the critical figure. A generator that meets the pump's starting watts but not its running watts would not be useful. Compare both figures before choosing.

Choosing the right size

The right generator size for a well pump depends on the pump's starting and running watts. The pump's nameplate or manual lists these figures. If the pump does not list starting watts, the pump maker can provide them. A licensed electrician can also help determine the pump's requirements.

Once you have the pump's figures, look for a generator whose starting watts are equal to or higher than the pump's starting watts, and whose running watts are equal to or higher than the pump's running watts. The generator's starting watts are the first figure in the title on this site. The running watts are in the details or on the maker's page.

If you plan to run other appliances at the same time as the pump, add their running watts to the pump's running watts, and their starting watts to the pump's starting watts. This is a general way to compare, but for a full load calculation, ask an electrician. For more on the difference, see running watts vs starting watts.

Fuel and type considerations

Well pumps run on electricity, so the generator's fuel type does not affect the pump. The fuel choice is about what you have available. Gasoline is a common fuel for portable generators. Dual fuel and tri fuel generators can run on propane or natural gas, which may be easier to store. The EIA explains that gasoline is a petroleum product, and natural gas is a fossil fuel. Propane is a hydrocarbon gas liquid.

The generator type also matters. Inverter generators are often lighter and more portable, while conventional open-frame generators may offer higher starting watts for the same price tier. For a well pump, the key is the watts figures, not the type. Compare the starting and running watts across types. See inverter vs conventional for a comparison.

If you are considering a standby generator for whole-home backup, the installation involves a licensed electrician and possibly a permit. The maker and the installer decide the correct size. This article focuses on portable generators for a well pump. For standby options, see best whole house generators.

Safety reminder

Generators produce carbon monoxide, an odorless, colorless gas that can be deadly. The CPSC warns that one generator produces as much CO as hundreds of cars. Never use a portable generator indoors, in a garage, basement, crawlspace, or shed. Use it outside, far from windows, doors, and vents. Follow the maker's manual and read the CPSC and CDC carbon monoxide pages for guidance.

Connecting a generator to your home's wiring is a job for a licensed electrician. Do not attempt to backfeed or use a dryer outlet. The electrician, the maker, and the local permit office decide the correct connection method.

What to pick for your situation

Questions

What are starting watts for a well pump?

Starting watts are the higher power draw for the brief moment the pump motor starts. They are always larger than running watts. The pump's nameplate or manual lists both figures.

How do I know the starting watts of my well pump?

Check the pump's nameplate or manual. If the starting watts are not listed, contact the pump maker. A licensed electrician can also help determine the pump's requirements.

Can a generator with lower starting watts still run a well pump?

No. If the generator's starting watts are lower than the pump's starting watts, the pump may not start. The generator's starting watts must meet or exceed the pump's starting watts.

Do I need to consider running watts for a well pump?

Yes. The generator's running watts must cover the pump's running watts. If the generator's running watts are lower, the pump may not operate steadily.

Can I connect a generator directly to my well pump?

Connecting a generator to your home's wiring is a job for a licensed electrician. Do not attempt to backfeed or use a dryer outlet. The electrician, the maker, and the local permit office decide the correct connection method.