How many watts does an electric water heater use?
A standard electric storage water heater uses about 4,500 watts while heating, which is the rating of the element inside the tank. At 240 volts that element draws 18.75 amps (4,500 divided by 240). Entry-level and smaller tanks sometimes use a 3,800-watt element, and some larger or faster-recovery models use 5,500 watts, so the practical range is 3,800 to 5,500 watts. The heating element is a simple resistance coil, so it draws its full rated power the instant it turns on, with no startup surge like a motor-driven appliance has.
Most 40 and 50 gallon tanks actually have two 4,500-watt elements, one near the top and one near the bottom, which leads people to assume the heater pulls 9,000 watts. It does not. The elements are non-simultaneous: the control wiring lets only one run at a time, the upper element first to recover the top of the tank, then the lower one. So the peak draw is still about 4,500 watts, not double that. That design is exactly why a single 30-amp, 240V circuit is enough.
The number that drives your power bill is not the 4,500-watt peak but how many hours the element actually runs. It cycles on to reheat the tank after a shower or a load of dishes, then shuts off and holds temperature, kicking back on now and then to make up standby heat loss. Across a full day the element is typically on for only a few hours total. To size a generator or an off-grid plan around it, use the nameplate on the tank and the solar panel calculator rather than guessing.
How many watts does a 50-gallon or tankless water heater use?
A 50-gallon electric water heater uses about 4,500 watts at the element, the same as a 40-gallon tank. Tank size changes how much hot water you can store and how long recovery takes, not the wattage of the element doing the heating. A bigger tank simply holds more hot water, so the element runs longer to reheat a drained 50-gallon tank than a 40-gallon one, which is why the larger tank uses a bit more energy over a day even though its instant wattage is identical.
An electric tankless (on-demand) water heater is a completely different animal: 18,000 to 36,000 watts, or 18 to 36 kW. Because it heats water instantly as it flows instead of keeping a tank hot, it has to dump enormous power into the water in real time. A whole-house electric tankless unit pulls 75 to 150 amps at 240 volts, usually across two to four double-pole breakers, and many homes need a 200-amp service or a panel upgrade to add one. Small point-of-use tankless heaters for a single sink are smaller, roughly 3,000 to 12,000 watts.
That gap matters enormously for backup power and solar. A 4,500-watt tank heater is a load a mid-size generator can handle; a 27,000-watt whole-house electric tankless heater is not, and it is effectively impossible to run off a battery or a portable solar generator. If you are on well water or off-grid and want on-demand hot water, a gas tankless or a tank paired with the sun is far more realistic than electric tankless. Our how many watts to run a house breakdown shows where a water heater sits against everything else on the panel.
How much electricity does an electric water heater use and cost?
A typical household's electric tank water heater uses about 10 to 15 kWh a day, roughly 4,000 to 5,000 kWh a year. Water heating is one of the largest slices of a home electric bill, usually second only to heating and cooling. The exact figure depends on how many people live there, how long the showers run, the incoming water temperature, and the tank's insulation, so a single person in a warm climate might use half that and a big family in a cold climate more.
At the 2026 US average residential rate near $0.17 per kWh, that works out to about $50 to $75 a month, or roughly $600 to $900 a year, just to heat water. These are estimates: your own rate and hot water habits move the number a lot, so treat them as a ballpark rather than a promise. If the relationship between the 4,500-watt rating and the kWh on your bill is confusing, our kW vs kWh and watts to kWh explainers untangle the power-versus-energy difference.
The cheapest ways to cut the cost are to use less hot water and to lose less heat. Set the thermostat to 120 degrees (the usual factory setting is 140, which wastes energy and scalds), insulate the first few feet of hot and cold pipe and the tank itself if it is an older uninsulated model, fix dripping hot taps, and install low-flow showerheads. A longer-term upgrade, a heat-pump water heater, cuts the energy use by two-thirds or more, which is covered below.
What size circuit and breaker does an electric water heater need?
A standard 4,500-watt electric tank water heater needs a dedicated 240-volt, 30-amp circuit, wired with 10-gauge wire and protected by a 30-amp double-pole breaker. A 30-amp, 240V circuit carries up to 7,200 watts, well above the element's 4,500-watt, 18.75-amp draw, which leaves the required headroom for a continuous load. A 5,500-watt element still fits on the same 30-amp circuit. The water heater gets its own circuit; it does not share with other appliances.
The breaker must match the wire feeding it. A water heater on 10-gauge wire takes a 30-amp breaker, not a larger one, because a bigger breaker would let the wire overheat before tripping, which is a fire hazard rather than extra capacity. Electric tankless units are the exception that proves the point: their 75-to-150-amp draw is exactly why they need heavy feeders and often a service upgrade, work that is squarely for a pro.
Installing or moving a water heater circuit means working inside the main service panel at 240 volts, which is licensed electrician territory and usually a permit, the same as wiring a 240V space heater or an electric dryer circuit. Swapping out the tank itself when the old one fails is a plumbing job most people hire out; the electrical connection behind it is not a DIY project.
Can you run a water heater on solar or a battery?
You can run an electric tank water heater on solar, but a resistance tank is one of the heaviest loads to carry on batteries, because 10 to 15 kWh a day of heating rivals the base load of the rest of the house combined. The smartest approach on a grid-tied system is to heat the tank in the middle of the day with a timer, while the panels are producing, so live solar does the heating instead of the battery or the grid at night. A simple 240V timer or a load controller on the water heater turns it into a daytime solar sink.
For off-grid or battery backup, the honest answer is that a standard resistance tank is a poor fit. A 100Ah, 12-volt battery holds only about 1 kWh, so it cannot make a dent in a day of water heating, and its inverter usually cannot supply 240 volts anyway; our what a 100Ah battery can run breakdown shows how much lighter the loads it suits really are. The two setups that actually work with solar are a heat-pump (hybrid) water heater, which draws only about 400 to 600 watts in heat-pump mode and uses a third to a quarter of the energy of a resistance tank, and a solar water heater with roof collectors that heat the water directly with sunlight and almost no electricity. Both are detailed in our solar water heaters guide.
A gas or propane tank water heater sidesteps the whole problem for backup, since it makes its heat from fuel and uses little or no electricity. If you want the sun to carry your hot water, size the load honestly with the solar panel calculator first, then decide between shifting a resistance tank to midday, switching to a heat-pump unit, or adding solar thermal. Trying to brute-force a resistance tank off a battery bank is how off-grid plans blow their budget.
Frequently asked questions
Will a 5,000 watt generator run a hot water heater?
Yes, a 5,000-watt generator can run a standard 4,500-watt electric tank water heater, as long as it is the generator's continuous (running) rating, not its peak, and the generator has a 240-volt outlet. There is no startup surge on a resistance element, so running watts is what counts. The catch is that the water heater uses nearly all of that 5,000 watts, leaving little for anything else, so you would typically run the heater on its own for a while, then switch to other loads.
How many watts does a 50 gallon electric hot water heater use?
About 4,500 watts at the heating element, the same as a 40-gallon tank, because element wattage does not change with tank size. A 50-gallon tank just holds more hot water and takes a little longer to recover, so it uses somewhat more energy over a day: roughly 11 to 15 kWh daily, or about 4,000 to 5,000 kWh a year for a typical household. Most 50-gallon tanks have two 4,500-watt elements, but only one runs at a time, so peak draw stays near 4,500 watts.
Will a 6,500 watt generator run a hot water heater?
Yes, comfortably. A 6,500-watt (running) 240V generator carries a 4,500-watt electric water heater with about 2,000 watts to spare for lights, a fridge, or a few outlets at the same time. It will not run a whole-house electric tankless heater, which needs 18,000 to 36,000 watts, but for a standard tank it has useful headroom. Confirm the generator has a 240V outlet and that 6,500 watts is its continuous rating, not its surge peak.
How much hot water does a 20 minute shower use?
A 20-minute shower with a standard 2.0 to 2.5 gallon-per-minute showerhead uses about 40 to 50 gallons of water, of which roughly 30 to 40 gallons is hot. That is most of a 50-gallon tank, which is why a couple of back-to-back long showers can run a tank out of hot water and make the element work hard to recover. A low-flow 1.8 GPM head cuts it to about 36 gallons total, one of the easiest ways to lower both water and water-heating costs.
Do gas water heaters use electricity?
Very little or none. A standard gas tank water heater with a standing pilot light uses no electricity at all; it makes its heat from gas and lights itself with the pilot. Models with electronic ignition or a powered damper use only a few watts, and gas tankless units use a bit more for their controls and sometimes a fan, but still only tens of watts. That tiny electrical draw is why a gas water heater keeps making hot water in a power outage and is trivial to back up compared with a 4,500-watt electric tank.