Sump Pump Generator: Sizing for Startup Surge

Why the Startup Surge Matters

A sump pump motor needs extra power for a brief moment when it turns on. This is called the starting surge or starting watts. The surge lasts only a second or two, but the generator must be able to deliver it or the pump may not start.

Generator listings show two figures: starting watts and running watts. The starting figure is the higher one, and it is the one that matters for a sump pump. If the generator's starting watts are lower than the pump's surge, the pump may stall or the generator may overload.

The EIA explains that electricity is measured in watts, and a watt is a unit of power. The pump's nameplate lists its running watts, but the surge is not always printed. The maker's manual or the pump's documentation usually states the starting surge.

Reading the Sump Pump Label

The sump pump's nameplate lists the voltage and the running watts or amps. Amps times volts gives watts, but the surge is separate. For a motor, the starting surge is often several times the running watts.

If the nameplate only shows amps, multiply the amps by the voltage (for example, 120 volts) to get running watts. Then check the pump's manual or the maker's website for the starting surge figure.

This site does not provide a wattage table or a sizing formula. The pump's label and the maker's documentation are the only sources for the exact numbers. For a general overview of how to compare generator sizes, see the generator wattage calculator article.

Matching Generator Listings to the Surge

When you read a generator listing, look for the starting watts figure. That is the number to compare with the pump's surge. If the listing shows only running watts, the starting figure is usually higher, but the listing may not state it.

Some generator titles list two figures, such as "5,500 starting watts / 4,500 running watts." The first figure is the starting watts. For a sump pump, the starting figure must be at least as high as the pump's surge.

If the listing does not state the starting watts, contact the maker or check the manual. This site compares listings on stated details only, so a missing figure is a reason to ask the maker. You can also learn more about how starting watts differ from running watts in the generator running vs starting watts article.

What Else to Consider

A sump pump is often one of several appliances you want to power during an outage. The generator's running watts must cover the total of everything running at once, plus the surge of the pump when it starts.

The Florida Division of Emergency Management advises checking your generator before the storm and connecting only essential appliances to avoid overloading. That guidance applies to any generator you choose.

For a home with a sump pump, a portable generator in the 3,000 to 5,000 watt range is a common starting point, but the exact size depends on the pump's surge and what else you plan to run. The guides below compare generators on stated details. See the best 3000 to 5000 watt generators for hurricanes guide for a starting point.

Comparing Fuel Types for Your Generator

Once you know the wattage you need, the next question is fuel. Gasoline is the most common, but dual fuel and tri fuel generators also run on propane or natural gas. The choice affects how you store fuel and how long you can run during an outage.

The EIA explains that gasoline is a fuel made from crude oil, while propane and natural gas are hydrocarbon gas liquids. Each fuel has different storage and supply considerations, but this site does not advise on fuel storage or supply.

If you are comparing fuel types, the dual fuel vs single fuel generator article explains the listing terms. For a generator that runs on multiple fuels, see the best dual fuel generator for Florida guide.

What This Site Cannot Say

This site does not promise that any generator will run a specific sump pump. The pump's label and the maker's documentation are the only sources for the surge figure.

This site also does not give advice on connecting a generator to your home's wiring. A licensed electrician, the maker, and the local permit office decide that. For more on that topic, see the generator transfer switch types article.

For safety, follow the maker's manual and read the CPSC and CDC pages on generator use. The Florida Division of Emergency Management also publishes generator safety guidance. See the generator carbon monoxide safety article for a summary of the official resources.

What to pick for your situation

Questions

What is the starting surge on a sump pump?

The starting surge is the extra power a sump pump motor draws for a moment when it turns on. It is higher than the running watts and can be several times that figure. The pump's nameplate lists running watts, but the surge is usually in the maker's documentation.

How do I find the starting watts for my sump pump?

Check the pump's nameplate for the running watts or amps. If only amps are shown, multiply amps by volts (usually 120) to get running watts. Then look in the pump's manual or on the maker's website for the starting surge figure.

What generator size do I need for a sump pump?

The generator's starting watts must be at least as high as the pump's surge. The running watts must cover the pump plus anything else you run at the same time. This site does not provide a sizing formula; use the pump's label and the maker's documentation.

Can a power station run a sump pump?

A power station's continuous output must cover the pump's running watts, and its peak output must cover the surge. Power station listings state continuous and peak watts. Compare those figures with the pump's numbers, and check the maker's documentation.

Why do generator listings show two watt figures?

The two figures are starting watts and running watts. Starting watts is the higher figure and covers the surge when motors start. Running watts is the continuous output. For a sump pump, the starting figure is the one that matters.