Short answer
120 F for most homes. The Department of Energy’s federal energy program says that for most residential uses the water heater should be set at 120 F. Homes that store water hotter for capacity or bacteria control can set the tank to 140 F and fit a thermostatic mixing valve that delivers 120 F at the taps, the approach FEMP cites from a Department of Defense facility specification. Check with a thermometer at the tap; dial markings are not exact.
Why 120 F
DOE’s Federal Energy Management Program says the temperature should be set at 120 F for most residential applications (FEMP). Lower settings cut standby heat loss and the risk of scalds, which rises quickly as water gets hotter. Children and older adults are most at risk.
When to store hotter
Legionella bacteria can grow in water heaters under some conditions, and the CDC says the key to preventing Legionnaires’ disease is controlling the growth and spread of the bacteria (CDC). FEMP notes a Department of Defense specification that stores water at 140 F and uses a thermostatic mixing valve set to 120 F for residential use. That setup gives both bacteria control at the tank and scald protection at the tap. ENERGY STAR notes some local codes and utility programs require a mixing valve with a water heater (ENERGY STAR).
See thermostatic mixing valves
How to set it
Measure first
Run hot water at the tap nearest the heater for two minutes and measure it in a cup with a cooking thermometer.
Gas tank
Turn the dial on the gas control valve at the bottom of the tank. Markings are often words or letters, not degrees; move it a small step at a time.
Electric tank
Switch off the breaker, remove both access covers and the insulation, and set the upper and lower thermostats to the same number with a screwdriver. Refit the insulation and covers before restoring power.
Recheck
Wait a few hours for the tank to settle, then measure again at the same tap and adjust.
What you need
Temperature and other problems
- Relief valve dripping? A setting that is too high is one cause: T&P valve guide.
- Running out of hot water? Turning it up is a short term fix; the real answer may be a larger first hour rating (size calculator), a flush, or a failed element (element guide).
Questions people ask
Is 120 or 125 F better for a water heater?
DOE’s federal energy program recommends 120 F for most homes. A few degrees higher can stretch hot water in a busy home, but every degree raises the scald risk and standby energy use.
Should I set my water heater to 140 F to prevent Legionella?
Hotter storage is used to limit Legionella growth in some settings; FEMP cites a 140 F storage setpoint with a mixing valve set to 120 F. If anyone in the home is at higher risk, ask your doctor or a plumber about storing hot and mixing down.
How do I check my water heater temperature?
Run hot water at the tap nearest the heater for a couple of minutes, then hold a cooking thermometer in a cup of it. Adjust the heater and recheck after a few hours.
Where is the temperature dial on an electric water heater?
Behind the upper and lower access covers, on each thermostat. Turn off the power first, then set both thermostats to the same temperature with a screwdriver.
Sources
Last reviewed October 29, 2026. Models, codes and listings change; check your heater’s manual and your local code, and follow the maker’s instructions.