The short answer: 120°F
The Department of Energy’s home energy checklist says to turn the water heater down to the warm setting, 120°F, to save energy and avoid scalding. The CPSC urges every household to do the same, and notes that most people hurt by tap water scalds are older adults and children under five.
How fast hot water burns
The CPSC’s figures for adults: third-degree burns after two seconds in 150°F water, six seconds at 140°F and thirty seconds at 130°F. Even at 120°F, five minutes can do it. A few degrees matter most for small children and older relatives.
The dial doesn’t tell you the whole story
Many gas controls show words or letters instead of degrees, and what an electric thermostat says isn’t always what reaches the tap. The CPSC’s way to know: hold a candy or meat thermometer under the hot tap first thing in the morning, or at least two hours after anyone has used hot water.
Gas or electric: where the setting lives
On a gas tank, the temperature dial is on the gas control at the bottom front of the heater. An electric tank usually has two thermostats, upper and lower, each behind its own access panel, and the CPSC says both should be set to the same temperature. Those panels also cover live 240-volt wiring and the heating elements, which our water heater repair page says to leave to us. If you open a panel at all, the breaker is off first, and you touch only the thermostat adjustment.
Tankless units
A tankless heater has no tank to keep hot. It heats water as it flows, to the temperature set on a wall controller or the unit’s display. Rinnai, for example, ships its residential units with a 120°F maximum; going higher means changing a setting inside the unit, which is a plumber’s job. Sizing and descaling are on our tankless water heater page.
The case for hotter: Legionella
Legionella, the bacteria behind Legionnaires’ disease, grow in water between 68°F and 122°F and fastest between 95°F and 115°F, according to OSHA. OSHA treats a heater running at 140°F or more, with water at the far faucets at 122°F or more, as low risk. That’s the tradeoff: hotter in the tank means more scald risk at the tap. If someone at home has a weakened immune system, ask their doctor. A plumber can add a mixing valve at the heater so the tank runs hotter while the taps get cooler water.
Sources: U.S. DOE, home energy checklist · CPSC, avoiding tap water scalds (Publication 5098) · OSHA, Legionellosis hazards · Rinnai tankless maintenance FAQ. Checked November 2026.
