How many watts does a sump pump use?
A home sump pump uses about 800 running watts for the common 1/3 HP size and around 1,050 watts for a 1/2 HP, drawn from a standard 120-volt outlet. Those are the input watts at the plug, which is what your meter and any inverter or generator actually see. Published figures vary a lot (a 1/3 HP pump is quoted anywhere from 400 to 900 running watts depending on the brand and head height), so treat 800 watts as the planning number for the typical home and read your own pump's label for the exact figure.
The number that matters more than running watts is the startup surge. A sump pump is an induction motor, so the instant it switches on it briefly demands two to three times its running watts to overcome inertia and get the impeller spinning. A 1/3 HP pump that runs on 800 watts can momentarily spike to 1,300 to 2,900 watts; a 1/2 HP pump surges to roughly 2,150 to 4,100 watts. The surge lasts a fraction of a second, but a battery inverter or generator that cannot supply it will stall or trip instead of starting the pump.
To pin down your own pump, find the nameplate amps on the motor housing or in the manual and multiply by 120 volts. A pump rated 7 amps at 120 volts is an 840-watt pump. Most residential units are 120-volt plug-in, not the 240-volt hardwired setup a well pump uses, which is good news for backup power: a sump pump plugs into a wall outlet, so running it from a power station is far simpler than wiring into a 240-volt circuit.
How many watts does a sump pump use by horsepower?
Sump pump power tracks motor size closely. A 1/4 HP pump runs on about 500 to 800 watts and surges to roughly 1,200 to 2,000 on start. A 1/3 HP pump, the most common home size, runs on about 800 watts with a startup surge near 1,300 to 2,900. A 1/2 HP pump runs on about 1,050 watts and surges to roughly 2,150 to 4,100. A 3/4 HP pump runs on about 1,400 to 1,800 watts with a surge past 3,000, and the heavy 1 HP units used in high-water-table homes draw more still.
Most houses do fine on a 1/3 HP pump, which clears a typical basement, and step up to 1/2 HP only for a deep pit, a high water table, or a long vertical run to the discharge point. Bigger is not automatically better: a pump that moves water faster than it comes in just cycles on and off more, which wears the motor and switch. There are two body styles at any horsepower. A submersible pump sits down in the pit, runs quieter, and is the modern default; a pedestal pump keeps the motor up on a shaft above the water, costs less, and is easier to service but louder. The wattage is about the same for a given horsepower either way.
For backup power planning the two numbers to carry forward are the running watts and the starting surge, and you size the inverter or generator around the surge. If you are adding a sump pump to an outage plan, treat a 1/3 HP pump as an 800-watt continuous load with a roughly 2,000 to 2,900-watt momentary surge, then run it alongside the rest of your loads through the solar panel calculator to size the battery and panels.
How much electricity does a sump pump use, and what does it cost?
A sump pump uses almost nothing most of the year and a real amount during a wet spell, because it only runs when water reaches the float. In dry weather it may not cycle for days, so its monthly cost rounds to zero. During steady rain or spring snowmelt it can kick on every minute or two for hours, and that is when it shows up on the bill. There is no single daily kWh figure the way there is for a refrigerator that cycles around the clock.
Put a number on it with the duty cycle. An 800-watt pump that runs 10 minutes an hour during a rainy day uses about 0.13 kWh an hour, roughly 3.2 kWh over 24 hours, which at the US average rate near 17 cents per kWh is about 55 cents for that day. A pump that short-cycles every minute in a flooding event uses far more and is also a sign of a problem: a stuck float, a pump that is undersized for the inflow, or a check valve letting water run back into the pit. To turn your own runtime into kWh and dollars, see watts to kWh.
Across a full year a sump pump in a normal basement typically costs only a few dollars, because the hours add up to so little. The cost is not the point with a sump pump. The point is that the pump runs when you need it, which is a reliability question, not an energy-bill question, and that is where backup power comes in.
Why does a sump pump need a backup power source?
A sump pump needs backup power because the storm that floods your basement is usually the same storm that cuts your electricity. Heavy rain, high wind, and lightning take down the grid at the exact hours the pump has the most water to move, so a sump pump on utility power alone protects you on sunny days and fails you on the one day it matters. A dead pump during a downpour means a flooded basement, which is why backup is standard advice for anyone in a wet area.
There are three common backups, and they are not equal. A battery backup system is a second DC pump (or a small inverter feeding the main pump) wired to a deep-cycle battery that takes over automatically when the power drops; it is the most popular choice and works anywhere. A water-powered backup pump uses your municipal water pressure to create suction and needs no electricity at all, which makes it the most reliable during a long outage, but it wastes a gallon or two of city water per gallon pumped and does nothing for a home on a private well with no city pressure. A portable generator or power station can run the existing pump but only if someone is home to start it and it can supply the surge.
The honest tradeoff is runtime versus independence. A battery backup runs out when the battery does, typically after several hours to a day of intermittent pumping, and then needs grid power or solar to recharge. A water-powered backup runs as long as the city water keeps flowing, which can outlast any battery, but only works on municipal water. Many people in serious flood zones run both: a battery system for the first hours and a water-powered pump as the never-dies fallback.
Can you run a sump pump on a battery or power station?
Yes, and a sump pump is one of the better matches for a portable power station or solar generator, because it is a 120-volt plug-in load and uses little total energy. The whole challenge is the startup surge, not the running watts or the daily kWh. You need an inverter or power station whose surge rating clears the pump's starting watts: for a 1/3 HP pump plan on an inverter that can deliver at least a 2,000 to 2,900-watt surge even though it only runs on 800, and a low-frequency (transformer-based) inverter handles motor inrush far better than a cheap high-frequency one.
Because the energy per cycle is small, a modest battery goes a long way. A 12-volt 100Ah battery holds about 1 kWh of usable energy, enough to run an 800-watt pump for roughly an hour of actual pumping, which during a storm that cycles 10 minutes per hour stretches to most of a day of coverage. A purpose-built DC backup sump pump sips even less, since it is a smaller low-voltage motor, and is often rated for thousands of gallons on one charge. See what a 100Ah battery can run for how that math shifts with the load and the inverter.
On solar, a sump pump is a load you cover from stored battery power, not from the panels in real time, because it runs in short bursts that no small array can feed directly, and the heaviest pumping happens during dark storm hours. The solar panels recharge the battery between storms and over the day. Size the battery for the number of hours you want to survive without the grid, add a solar battery with enough surge output, and run the whole plan through the solar panel calculator alongside everything else in the house. Wiring any backup into the pump circuit is licensed electrician work.
What circuit and outlet does a sump pump need?
A sump pump needs its own dedicated 120-volt, 15 or 20-amp circuit on a GFCI outlet. The dedicated circuit keeps the pump from sharing a breaker with other loads that could trip it off right when it needs to run, and the GFCI (ground-fault) protection is required because the pump is an electric motor sitting in water, where a fault is a genuine shock hazard. This is the one real electrical catch with sump pumps, and it is exactly why the install is electrician work, not a project to improvise.
At 800 to 1,050 running watts a sump pump draws only about 7 to 9 amps at 120 volts, well within a 15-amp circuit, so the running load is not the issue; the dedicated circuit is about reliability and code, not capacity. Never run a sump pump on an extension cord as a permanent setup, and if you use one in a pinch it must be a heavy-gauge cord rated for the load, because a thin cord drops voltage and makes the motor run hot.
Unlike a dryer, water heater, or most well pumps, a sump pump never needs a 240-volt circuit. It is a simple 120-volt plug-in appliance, which is what makes backing it up with a battery or power station so much easier than backing up a 240-volt load. Give it a dedicated GFCI circuit and a backup power source, and the hard part of a sump pump is solved.
Frequently asked questions
Will a 1500 watt generator run a sump pump?
A 1,500-watt generator runs a small 1/4 or 1/3 HP sump pump only if its surge rating covers the pump's startup spike, which is 2 to 3 times the running watts. A 1/3 HP pump runs on about 800 watts but can surge to 1,300 to 2,900 watts for an instant, so a 1,500-watt unit with a higher surge number can start it, while one capped near 1,500 of surge may stall. It will not reliably start a 1/2 HP pump, which can surge past 2,000 watts. Match the generator's surge rating to the pump's starting watts, not its running watts.
How many watts to run a 3/4 HP sump pump?
A 3/4 HP sump pump runs on about 1,400 to 1,800 watts and surges to well over 3,000 watts for the moment the motor starts. Size any generator or inverter to that starting figure: a 4,000 to 5,000-watt unit handles a 3/4 HP pump comfortably, with headroom for the surge and for anything else running at the same time. The running draw is the easy part; the inrush is what forces the bigger power source.
How long will a 100Ah battery run a sump pump?
A 12-volt 100Ah battery holds about 1 kWh of usable energy, enough to run an 800-watt (1/3 HP) sump pump for roughly one hour of actual pumping time. Because a sump pump only runs when the pit fills, that stretches much further in practice: a pump cycling 10 minutes per hour during a storm gets most of a day of coverage from one battery. A dedicated 12-volt DC backup pump draws less and lasts longer. Add an inverter whose surge rating clears the pump's startup spike, since the surge is the limit, not the battery.
Does a sump pump use a lot of electricity?
No, a sump pump uses very little electricity overall, usually only a few dollars a year, because it runs only when water reaches the float. It can draw a real amount during steady rain or snowmelt, when it may cycle every minute or two for hours, but in dry weather it may not run for days. The reason sump pumps get attention is reliability during outages, not energy cost: the pump has to run during the storm that often takes the grid down with it.
Can a sump pump run on solar power?
Yes, but through a battery, not straight off the panels. A sump pump runs in short bursts and does the heaviest work during dark storm hours, so solar's job is to keep a battery charged between and during storms while the battery supplies the pump. Size the battery for the hours of outage you want to cover, use an inverter whose surge rating clears the pump's startup spike, and plan the array with the solar panel calculator. A dedicated DC backup pump on a solar-charged battery is the cleanest off-grid setup.