What temperature should a water heater be set to?
Short answer: For most homes, set the water heater to 120°F. The U.S. Department of Energy says most households only need 120°F, and the CPSC urges lowering heaters to 120°F to cut scald risk. Some homes may need more, such as a dishwasher without a booster heater, or a household with Legionella concerns.
Is 120°F the right water heater temperature?
For most households, yes. The Department of Energy (DOE) says some manufacturers set thermostats at 140°F, but most homes only need 120°F. DOE adds that a lower setting also slows mineral buildup and corrosion in your water heater and pipes.
The Consumer Product Safety Commission (CPSC) goes further. It urges all users to lower their water heaters to 120°F. The CPSC notes that most tap water scald injuries and deaths involve older adults and children under five.
How fast can hot tap water burn you?
The CPSC gives these exposure times for third-degree burns in adults:
| Water temperature | Time to a third-degree burn (CPSC) |
|---|---|
| 150°F (65.6°C) | About 2 seconds |
| 140°F (60°C) | About 6 seconds |
| 130°F (54.4°C) | About 30 seconds |
| 120°F (48.9°C) | About 5 minutes |
The jump from 120°F to 140°F cuts the safe window from minutes to seconds. That matters most for small children, older adults, and anyone who can’t pull away quickly.
When might you need a higher setting?
Dishwashers. DOE says a dishwasher without a booster heater may need water between 130°F and 140°F for best cleaning. Check your dishwasher manual first.
Legionella concerns. OSHA’s workplace guidance warns that water heaters kept below 140°F, with scale and sediment, may foster Legionella growth. For buildings it advises storing hot water at 140°F or higher and delivering at least 122°F to outlets. That guidance is written for workplaces, not homes.
If someone in your home has a weakened immune system, ask your doctor or a licensed plumber. Storing water hotter raises scald risk. A plumber can tell you whether a thermostatic mixing valve, which blends hot and cold water before it reaches the tap, fits your system.
How do you check your water temperature?
DOE recommends this method:
- Run hot water at the tap farthest from the water heater.
- Hold a cooking or candy thermometer in the stream and note the reading.
- Adjust the thermostat if needed.
- Wait a couple of hours, then measure again at the same tap.
The dial marking may not match the water at the tap, so trust the thermometer reading.
How do you adjust a gas vs electric water heater?
Gas tanks. Follow your owner’s manual. The control knob is often on the gas valve near the bottom of the tank. Turn it in small steps, then recheck at the tap.
Electric tanks. The thermostats sit behind access panels. DOE says to shut off electricity to the water heater before removing or opening the panels. Turn off the breaker, then follow the manual. Close the panels before restoring power.
If you smell gas, see scorch marks, or aren’t comfortable working near wiring, stop and call a professional.
How much do you save by lowering the temperature?
DOE says a water heater set at 140°F can waste $36 to $61 a year in standby heat losses. That is heat leaking from the tank and pipes while nobody uses water.
You also save on water used without mixing, such as in a washer on the hot setting. Heating water takes about 8.34 BTU per gallon per °F:
- 8.34 lb/gal × 10°F × 1 BTU/(lb·°F) = 83.4 BTU
- 83.4 BTU ÷ 3,412 BTU/kWh = 0.0244 kWh per gallon, per 10°F
The table assumes an electric resistance heater, which converts electricity to heat at close to 100% efficiency. Real savings vary with tank and pipe losses. It covers only water drawn straight from the tank, not water mixed at the shower.
| Electricity rate | Per gallon, 10°F less | 20 gal/day for a year, 10°F less |
|---|---|---|
| 12¢/kWh | 0.29¢ | $21.41 |
| 15¢/kWh | 0.37¢ | $26.77 |
| 18¢/kWh | 0.44¢ | $32.12 |
| 25¢/kWh | 0.61¢ | $44.61 |
| 30¢/kWh | 0.73¢ | $53.53 |
At 18¢: 0.0244 kWh × 20 gal × 365 days = 178 kWh, and 178 × $0.18 = about $32. Use the rate on your own bill for a closer estimate.
For more ways to cut bills, see how to lower your electric bill in winter.
Quick answers
Is 140°F too hot for a water heater? For most homes, yes. CPSC says 140°F water can cause a third-degree burn in about 6 seconds. Use it only for a specific need, with scald protection.
What is the factory setting on a water heater? It varies. DOE says some manufacturers set thermostats at 140°F, so check yours with a thermometer.
What should I do with my water heater on vacation? DOE suggests turning the thermostat to its lowest setting or turning the heater off.
Does 120°F kill Legionella? OSHA guidance links Legionella growth risk to storage below 140°F. If someone is at higher risk, ask a doctor or licensed plumber about safe options.
Why is my hot water still lukewarm after I raised the setting? Wait a couple of hours before rechecking, as DOE advises. If it stays lukewarm, have the heater inspected by a qualified technician.