The hot water in your home is probably hotter than necessary. Most heaters are factory set at 140°F, and this high setting is only needed if you have a dishwasher without a booster heater. Turn the temperature down to 120°F (medium setting on a gas heater dial), and you’ll cut your water-heating costs by 6 to 10 percent. Most electric heaters have both an upper and a lower thermostat to adjust. For safety, turn off the circuit breaker to your water heater before adjusting the thermostat.
If you have a dishwasher without a booster heater, it may require a water temperature within a range of 130ºF to 140ºF for optimum cleaning. And while there is a very slight risk of promoting legionellae bacteria when hot water tanks are maintained at 120ºF, this level is still considered safe for the majority of the population. If you have a suppressed immune system or chronic respiratory disease, you may consider keeping your hot water tank at 140ºF. However, this high temperature significantly increases the risk of scalding. To minimize this risk, you can install mixing valves or other temperature-regulating devices on any taps used for washing or bathing.
If you plan to be away from home for at least 3 days, turn the thermostat down to the lowest setting or completely turn off the water heater. To turn off an electric water heater, switch off the circuit breaker for the water heater. For a gas water heater, make sure you know how to safely relight the pilot light before turning it off.