What Temperature Should You Set Your Water Heater?
Most water heaters ship set to 140°F, but the U.S. Department of Energy recommends 120°F for the right balance of scald safety and energy savings. There's a real trade-off with Legionella bacteria risk at the lower setting -- see below. Here is how to choose and change it.
The Recommended Setting: 120°F
120°F is hot enough for showers, dishes, and laundry, while reducing the risk of scalding (especially for kids and older adults) and cutting standby energy loss. Every 10°F lower saves roughly 3-5% on water heating costs.
When to Go a Bit Higher
The CDC's actual Legionella-prevention guidance is more strict than a simple '120°F is fine' framing suggests: Legionella grows best between 77-113°F, and the CDC recommends storing hot water at 140°F or higher specifically to kill it, treating 120°F as closer to the upper end of the risk zone than a safe bacteria-control setting. If someone in the home is immunocompromised or elderly, if the home has low-use fixtures or a large plumbing system, or if you have a dishwasher without its own booster heater, storing at 140°F is the safer choice for bacteria control -- but 140°F at the tap is a real scald risk. The standard solution is a thermostatic mixing valve: it lets the tank store water at 140°F (Legionella-safe) while blending it down to a safe delivery temperature at each fixture, giving you both protections instead of choosing one.
How to Change It
On a gas heater, turn the dial on the thermostat/gas valve at the bottom. On an electric heater, turn off the breaker, remove the access panel(s), peel back insulation, and adjust the thermostat dial(s) with a flathead — set both upper and lower to the same temperature. Wait a few hours and check the temperature at a tap with a thermometer.
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FAQ
140°F delivers hotter water but raises scald risk (a serious burn in seconds) and energy bills. 120°F is the recommended balance for most homes.
Yes. Dropping from 140°F to 120°F can cut water-heating energy use noticeably, often 6-10%, with no real loss of comfort.
Sources
Documents this guide was checked against. How we verify.
Always unplug an appliance and shut off its water supply before servicing. This guide is informational and not a substitute for a qualified technician.