Why is 120°F the standard recommendation?
The Department of Energy's Federal Energy Management Program puts it plainly: for most residential applications, set the temperature at 120°F. The U.S. Consumer Product Safety Commission (CPSC) urges all users to lower their water heaters to 120°F, noting that the lower setting prevents accidents and also conserves energy and saves money.
The CPSC says the majority of injuries and deaths from tap-water scalds involve older adults and children under five. It describes 120°F, or 49°C, as a setting that may be necessary for residential water heaters to reduce or eliminate the risk of most tap-water scald injuries.
How fast can hot tap water burn?
The CPSC's scald figures show how quickly a few degrees make a difference for most adults. Because older adults and young children account for most scald injuries, homes with either deserve extra care.
- 150°F water: third-degree burns in about two seconds.
- 140°F water: burns with about a six-second exposure.
- 130°F water: burns with about a thirty-second exposure.
- 120°F water: a five-minute exposure could still cause third-degree burns, which is why the CPSC says to hand-test water before bathing infants and young children.
When might a hotter setting make sense?
Hot water systems can grow Legionella, the bacteria behind Legionnaires' disease. The CDC says keeping a home water heater between 130°F and 140°F can kill germs like Legionella, but that a higher setting increases the risk of burns. The CDC suggests asking your healthcare provider about your own risk of getting sick from Legionella when deciding whether a higher setting is right for your household.
If you do set the heater above 120°F, the CDC advises using thermostatic valves that mix cold and hot water at the tap to prevent burns, especially in homes with young children or older adults. The Department of Energy's guidance makes a similar point for buildings that need 140°F storage: install a tempering valve downstream of the heater and set it to deliver 120°F.
Commercial kitchens, clinics and other businesses may have their own code or health department requirements for hot water temperatures. Check those rules before changing a commercial heater's setting.
How do you check and adjust the temperature?
Thermostat markings do not always give a precise temperature, so a thermometer at the tap is the reliable check. Where precise temperatures are not given, the CPSC recommends holding a candy or meat thermometer under the faucet, first thing in the morning or at least two hours after anyone has used hot water. If the reading is too high, adjust the thermostat according to the manufacturer's instructions and check again.
- Gas water heaters: thermostats differ by model, so the CPSC suggests following the manufacturer's instructions or asking your gas utility.
- Electric water heaters: the CPSC says to shut off power at the circuit breaker first. Most electric tanks have two thermostats, upper and lower, behind access panels, and both must be set to the same temperature for proper operation.
- Apartments and condos with central hot water: the CPSC suggests contacting the building manager about lowering the tap temperature.
- After any change, wait at least two hours without using hot water, then test at the tap again.
Will 120°F be hot enough for dishes and laundry?
For most households, yes. The CPSC's advice is to lower the thermostat to the lowest setting that still satisfies hot water needs for the clothes washer and dishwasher. If an appliance manual lists a minimum water temperature, use that as your floor. If you regularly run short of hot water after lowering the setting, have the heater checked rather than simply turning the thermostat back up, so the scald protection stays in place.
Does the setting matter for tankless and heat pump models?
If your tankless heater has a temperature control, set it to 120°F following the manufacturer's instructions and confirm with a thermometer at the tap. Heat pump water heaters add a mode choice as well. The Department of Energy recommends setting a heat pump water heater to the mode that best meets your hot water demand, typically efficiency or hybrid, and reminds owners that heat pump models have a filter that must be cleaned regularly.
Whatever type you own, the CDC also recommends flushing the water heater regularly, noting that most manufacturers recommend once a year, to help prevent germ growth and help the heater last longer.
Common questions
Does lowering my water heater to 120°F save money?
The CPSC says lowering the setting to 120°F conserves energy and saves money in addition to preventing scalds, and the Department of Energy recommends 120°F for most homes. Savings depend on how much hot water your household uses.
Is 140°F safer because it kills bacteria?
The CDC says 130°F to 140°F can kill Legionella, but it raises the burn risk. If you choose a higher setting, the CDC recommends thermostatic mixing valves at the taps, and it suggests asking your healthcare provider about your risk.
How do I measure the hot water temperature?
The CPSC suggests holding a candy or meat thermometer under the faucet first thing in the morning or at least two hours after hot water was last used, then adjusting the thermostat and testing again.
Why does my electric water heater have two thermostats?
The CPSC says most electric water heaters have two thermostats behind upper and lower access panels, and both must be set to a common temperature for proper operation. Turn off power at the breaker before opening the panels.