Water Heater Temperature Setting: Why 120 °F

The recommendation

The Department of Energy's Energy Saver guide lists four ways to cut water heating bills: use less hot water, turn down the thermostat on the water heater, insulate the heater and pipes, or buy a more efficient model. For the thermostat its advice is to set the water heater to 120 °F, a temperature it calls safe for most of the population. The same guide puts water heating at about 18 percent of a home's energy use, the second largest energy expense after heating and cooling.

The Consumer Product Safety Commission gives the same number for a different reason. Its childproofing guide says that to prevent burns, the temperature on your water heater can be set to 120 °F or lower, and that anti-scald devices for faucets and showerheads can also help.

What 18 percent means on your bills

The share is easiest to see with an example. If a household spends $2,000 a year on all home energy, about 18 percent of that, or $360, goes to hot water. The insulation steps in the Energy Saver guide then scale from there: 7 percent of that amount is $25 and 16 percent is $58 a year. Your own split depends on the fuel, the number of people and how much hot water they use, so treat the 18 percent as a national rule of thumb, not a measurement of your house.

Common settings in Fahrenheit and Celsius

If your dial shows marks rather than degrees, measure at the tap as described below. The temperature converter handles any value; the common ones are here.

How to check it at the tap

The dial is only an approximation, so measure. Pick the tap closest to the water heater. Run the hot water until it stops getting warmer, then hold a cooking thermometer in the stream or fill a cup and measure right away. If the reading is well above 120 °F, turn the dial down a little, wait a few hours, and measure again. Mark the dial position that gave you the right reading so you can find it later. Follow the maker's manual for how to reach and adjust the thermostat on your model.

The dishwasher exception

Some dishwashers rely on the water heater for hot water. The Energy Saver guide says that if your dishwasher has an internal heating element that boosts water temperature, you can set your water heater to 120 °F, and to check the dishwasher manual for your model. If it has no booster, the manual will say what inlet temperature it needs.

The energy arithmetic

Heating water follows one rule. The Energy Information Administration defines a Btu as the heat that raises one pound of water by 1 °F, and a gallon of water weighs about 8.34 pounds. So:

Divide by 3,412 to get kWh. For an electric resistance tank, the EIA describes resistive elements as virtually 100 percent efficient, so the kWh in roughly equals the heat in the water, before heat lost from the tank. The table heats 50 gallons from an example 50 °F cold supply to each setting and prices it at the August 2026 US average of 18.16 cents per kWh.

Read this table with care. It shows the heat in water drawn straight from the tank at that temperature, as in a hot wash cycle. At a shower you mix hot with cold to reach the same comfortable temperature whatever the tank setting, so a lower setting does not cut that energy one for one. The Department of Energy does not give a single saving per degree in its guide; it gives savings for specific steps, such as 7 to 16 percent from insulating a tank that is warm to the touch and another 3 to 4 percent a year from insulating hot water pipes, which it says also lets you lower the temperature setting. Use the energy converter for Btu, kWh or therms and the electricity cost calculator for your own rate.

The temperature on the label

The yearly cost on a water heater's EnergyGuide label comes from a federal test that feeds the heater water at 58 °F and sets it to deliver water at 125 °F, give or take 5 degrees. That is a rise of 67 °F, which takes 0.164 kWh per gallon. If your setting is lower and your cold water warmer, your cost per gallon will be lower than the test assumes. The EnergyGuide label guide shows how to rescale the label's dollar figure to your own rate.

Tank vs tankless, briefly

A tankless heater has a set point too, but it heats water only as it flows, without a storage tank. The Energy Saver guide says gas on-demand water heaters can be 24 to 34 percent more energy efficient than conventional storage tanks for homes that use 41 gallons or less of hot water a day, and 8 to 14 percent for homes that use around 86 gallons a day. If you need several taps at once, it notes you may need two or more units. For sizing either type, see what size water heater do I need.

Steps

• Measure the hot water at the nearest tap.
• Turn the dial toward 120 °F and measure again after a few hours.
• Check the dishwasher manual for its inlet temperature or booster heater.
• Insulate a warm tank and exposed hot water pipes, following the maker's instructions.
• Write the final setting on the tank.

Frequently asked questions

Sources

• US Department of Energy, Energy Saver guide (2022 edition): set the water heater to 120 °F; water heating about 18% of energy use; tank and pipe insulation savings; dishwasher booster note; tankless 24% to 34% and 8% to 14% more efficient
• US Consumer Product Safety Commission, Childproofing Your Home: water heater can be set to 120 °F or lower to prevent burns; anti-scald devices for faucets and showerheads
• 10 CFR 430, subpart B, appendix E (eCFR): water heater test with supply water at 58 °F and delivery at 125 °F plus or minus 5 °F
• US Energy Information Administration, British thermal units: 1 Btu raises one pound of water by 1 °F; 1 kWh = 3,412 Btu
• US Energy Information Administration, Updated Buildings Sector Appliance and Equipment Costs and Efficiencies, appendix B (2023): resistive heating elements virtually 100% efficient
• US Energy Information Administration, Electric Power Monthly, table 5.6.A: average residential price, August 2026 (18.16 cents per kWh)
• NIST Chemistry WebBook, water at atmospheric pressure (density 62.367 lb per cubic foot at 60 °F, about 8.34 lb per US gallon of 231 cubic inches)

Written by Tobias. Updated November 2, 2026.