Water heating is usually the second largest line on a household electricity bill, behind heating and cooling and ahead of everything else. It is also the one people never think about, because the appliance sits in a closet doing its job silently and there is no thermostat on the wall to fiddle with.
A standard electric tank water heater uses a 4,500 W element that runs roughly three hours a day for an average household. That is about [hed_cost appliance=”electric-water-heater” period=”day”] a day at [hed_var key=”us_rate_cents” format=”cents”] per kWh, [hed_cost appliance=”electric-water-heater” period=”month”] a month, and [hed_cost appliance=”electric-water-heater” period=”year”] a year. Households with teenagers, long showers or a dishwasher running nightly will be well above that.
Two elements, one at a time
Tank heaters have two elements, upper and lower, and they do not run at the same time. The control alternates between them, so a heater with two 4,500 W elements still only draws 4,500 W. The element runs whenever the tank temperature drops below setpoint, which happens when you draw hot water and, more slowly, as the tank loses heat to the room through its insulation.
That second part is standby loss, and on an older tank it can be a fifth of the total. A tank installed in an unheated garage or crawlspace loses noticeably more than the same tank in a conditioned utility room.
[hed_wattage_matrix appliance=”electric-water-heater”]What each shower actually costs
Element runtime tracks hot water use almost linearly. Rough figures per event, at 4,500 W:
- A ten-minute shower reheats roughly 17 gallons, which is about 25 minutes of element time, or [hed_cost appliance=”electric-water-heater” hours=”0.42″ period=”day”].
- A dishwasher cycle drawing hot water costs roughly a third of that on top of the dishwasher own element.
- A hot-water clothes wash is the most expensive laundry setting by a wide margin, which is why cold-water detergent exists.
Multiply by the number of people in the house and the picture assembles itself quickly.
[hed_hours_matrix appliance=”electric-water-heater” hours=”1,2,3,4,5,6″]Water heater cost across electricity rates
Three hours of element time a day, every common rate.
[hed_rate_matrix appliance=”electric-water-heater”]Water heater running cost by state
Same tank, same household, different tariff.
[hed_state_costs appliance=”electric-water-heater”]Six changes worth making
- Set the thermostat to 120 degrees. Many are shipped at 140. Every 10 degrees of setpoint reduction cuts standby loss by around 4 percent, and 120 is the temperature health authorities recommend anyway. Below 120 you start risking bacterial growth in the tank, so 120 is the floor, not a starting point for further cuts.
- Insulate the first six feet of hot and cold pipe. Pipe sleeve is inexpensive and reduces the heat that walks out of the tank through the plumbing.
- Add a tank blanket if the tank is warm to the touch. Modern tanks are well insulated and gain little; a pre-2005 tank often gains a lot. Do not cover the top of a gas unit.
- Fix dripping hot taps. A hot tap dripping once a second is heating water that goes straight down the drain.
- Flush sediment annually. Sediment insulates the lower element from the water, so it runs longer to achieve the same result.
- Put it on a timer only if you have a predictable schedule. Timers save standby loss but a tank that has cooled fully takes real energy to bring back. The savings are modest and the complaints about cold showers are not.
The heat pump water heater question
A heat pump water heater does the same job by moving heat from the surrounding air into the tank rather than making heat with an element. It uses roughly a third of the electricity for the same hot water, which turns a [hed_cost appliance=”electric-water-heater” period=”year”] annual cost into something closer to [hed_cost appliance=”heat-pump-water-heater” period=”year”].
The catches are real. They cost more up front, they need roughly 700 to 1,000 cubic feet of space around them to draw heat from, they cool and dehumidify the room they sit in, and they are audible. In a garage in a warm climate they are close to a free win. In a small utility closet in a cold basement they are a poor fit. Our heat pump water heater savings calculator runs the comparison with your own numbers.
How this compares to everything else you plug in
Per hour of element time against the other large loads in the house.
[hed_compare_table appliances=”electric-water-heater,heat-pump-water-heater,clothes-dryer,dishwasher,electric-oven,washing-machine”]Questions people actually ask
[hed_faq]How much does it cost to run an electric water heater per month?About [hed_cost appliance=”electric-water-heater” period=”month”] for an average household at the US average rate, based on roughly three hours of element time a day. Larger households commonly run 50 to 100 percent higher.
How many watts does a water heater use?Most residential electric tank heaters use 4,500 W elements, with a range from 3,000 W in small tanks to 5,500 W in large ones. Only one element runs at a time, so the tank draw is the single element rating, not the sum.
Is it cheaper to turn the water heater off when away?For trips of several days, yes. Most units have a vacation setting that holds a low temperature without letting the tank go cold. For a single night away it is not worth it.
What temperature should an electric water heater be set to?120 degrees Fahrenheit. It is hot enough to be safe from bacterial growth, reduces scald risk, and cuts standby losses compared with the 140 degree factory default.
Does a tankless electric water heater cost less to run?It removes standby loss, so it uses somewhat less energy overall. It does not change the energy needed to heat the water itself, which is most of the cost. Electric tankless units also draw enormous instantaneous power, often 18,000 to 36,000 W, which frequently requires a service upgrade.
Why did my electricity bill jump with no change in habits?A failed lower element or a stuck thermostat can leave the upper element running far more than it should. If the bill rose and the hot water got worse at the same time, the water heater is the first thing to check.[/hed_faq]
Related running costs
[hed_related appliances=”heat-pump-water-heater,tankless-water-heater,dishwasher,washing-machine,clothes-dryer”]Running it on solar
A electric water heater uses [hed_daily_energy appliance=”electric-water-heater”] a day, which needs about [hed_panels_needed appliance=”electric-water-heater”] standard 400 W panels. Full array, battery and inverter sizing is on how many solar panels to run a electric water heater.