What temperature should my water heater be set to?

Most tanks ship set around 140°F, which is hotter than most households need. The common recommendation is 120°F, and understanding why involves three competing concerns pulling in different directions.

The case for lower

Scald time drops off a cliff as temperature rises. At 120°F it takes minutes of exposure to cause a serious burn; at 140°F it takes seconds. That difference matters enormously in a house with small children or older adults. Lower temperature also means less standby heat loss — the tank is fighting a smaller gap against room temperature all day, every day.

The case for higher

Legionella bacteria can grow in water sitting below roughly 120°F. For most healthy households this is not a practical concern at 120°F, which is why that number is the usual recommendation. But for homes with immune-compromised residents, guidance sometimes shifts to storing at 140°F and installing thermostatic mixing valves so the water reaching the taps is still tempered down to a safe delivery temperature. That gets you both properties at once.

How to change it

• On an electric heater, the thermostats sit behind access panels and require shutting off the breaker first — there are live terminals behind those covers.
• On a gas heater, the dial is usually on the control valve at the base, often marked with vague settings rather than degrees.
• Either way, verify with a thermometer at the tap furthest from the tank after a few hours, rather than trusting the dial.

A practical note

If hot water runs out too quickly, turning the temperature up is a tempting fix, and it does work — hotter stored water stretches further once mixed. But it trades scald safety for capacity. If the tank is genuinely undersized for the household, that is the actual problem to solve.

If the dial is unmarked or the heater is electric and you are not comfortable behind the panel, this is a small and inexpensive thing to have a plumber set correctly once.