Home / Generators

Generator for a sump pump: size it for the start, not just the run

By the Plain Prepper editors. Updated 2026-10-15.

We research products from makers' specs, manuals and safety agencies; we do not run hands-on tests. Links to Amazon may earn us a commission at no cost to you. How this works.

Quick answer

Champion's wattage chart lists a 1/2 HP sump pump at 800 to 1,050 running watts and 1,300 to 2,150 starting watts, and a 1/3 HP pump at 500 to 800 running and 1,000 to 1,600 starting. Size the generator by adding up the running watts of everything you will run, then adding the largest single starting wattage. A pump alone fits a 2,500 starting watt inverter. A pump plus a refrigerator calls for a larger unit.

Sump pump wattage from Champion's chart

Appliance	Running watts	Starting watts
Sump pump, 1/3 HP	500 to 800	1,000 to 1,600
Sump pump, 1/2 HP	800 to 1,050	1,300 to 2,150
Refrigerator	150 to 400	800 to 1,200
Freezer	100 to 500	500 to 1,000

These are typical ranges. Your pump's own label or manual is the better number; Champion notes that if only volts and amps are listed, volts times amps gives watts.

Do the sizing math

Champion's method: add the running watts of everything you will run, then add the single highest starting wattage. Using the top of each range:

• 1/2 HP pump alone: it must start at up to 2,150 W and run at up to 1,050 W. Champion's 201317 lists 2,500 starting and 1,850 running watts, which covers it.
• Pump plus refrigerator: running 1,050 + 400 = 1,450 W. Add the largest start, 2,150 W, and the peak is 3,600 W. That is beyond the 201317's 2,500 starting watts, but within the 201050's 4,000.
• On propane: Champion says propane typically gives about 10% less output. The 201050 lists 2,700 running watts on propane, still above 1,450.

Champion also suggests choosing a generator that exceeds your calculated need by a safe margin.

Connecting the pump

• Plug-in pumps: CPSC says to plug appliances into heavy duty, outdoor-rated extension cords with a wire gauge adequate for the load and a grounding prong, then plug the cords into the generator.
• Hard-wired or circuit-fed pumps: Champion says connecting a portable generator to a home's wiring requires a manual transfer switch installed by a licensed electrician; never backfeed through an outlet.
• Starting order: Champion's operator manual says to let the engine stabilize and warm up for a few minutes after starting, then plug in loads.

See our cord for a generator guide for matching cords to outlets.

Where to run a generator during a storm

Sump pumps work hardest during heavy rain, which is exactly when generator placement is hardest:

• Outdoors only: CPSC says never to run a portable generator indoors, including garages, basements and sheds, even with ventilation, and to keep it at least 20 feet from the home.
• Away from openings: NFPA says to keep generators away from windows, doors and vents.
• Keep it dry: CPSC says consumer generators are not weatherproof and to wait for rain to pass. If storms are likely, plan the outdoor spot in advance; see our generator cover guide for maker-made covers.
• CO alarms: both picks list Champion's CO Shield automatic shutoff, but keep working carbon monoxide alarms in the home as well.

Generator or battery backup pump?

A generator restores power to your main pump, but it needs someone to set it up, refuel it and run it safely outside. Basement Watchdog says its backup pump's control box monitors the system and takes over if the power goes out or the main pump fails. Basement Watchdog, for example, lists its Special CONNECT backup pump at 2,600 gallons per hour at 0 feet and 1,850 at a 10 foot lift. You can also use both: the battery pump covers the first hours, and the generator keeps the main pump and freezer going in a long outage. See our battery backup for sump pump guide.

What to look for when you buy

Questions people ask

What size generator do I need for a sump pump?

By Champion's chart, a 1/2 HP pump needs up to 2,150 starting watts and 1,050 running watts; a 2,500 starting watt generator covers the pump alone.

Can a 2000 watt generator run a sump pump?

Check the pump: Champion lists 1/3 HP pumps at up to 1,600 starting watts and 1/2 HP pumps at up to 2,150, so a 1/2 HP pump may exceed it.

Can I run a generator in the garage for my sump pump?

No; CPSC says never to use a portable generator in a garage, basement or shed, and to keep it 20 feet from the home.

Will a generator run a sump pump and refrigerator?

Using Champion's method and top-of-range figures, that pair peaks around 3,600 W, so plan on about 4,000 starting watts.

Sources

• Generator Wattage Chart, Champion Power Equipment
• What Size Generator Do I Need?, Champion Power Equipment
• 201317 2500W Inverter, Champion Power Equipment
• 201050 4000W Dual Fuel Inverter, Champion Power Equipment
• Surviving the Aftermath of a Hurricane (safety alert), U.S. Consumer Product Safety Commission
• Generator safety tips, National Fire Protection Association
• Special CONNECT Battery Backup Pump, Basement Watchdog
• 201277 Dual Fuel Generator Operator's Manual, Champion Power Equipment

Sources checked 2026-10-15.