What Temperature Should a Water Heater Be Set At?

By Ray Bennett · Updated 2 October 2026 · 5 min read · Checked against the sources at the end

What Temperature Should a Water Heater Be Set At?

Short answer

120 degrees suits most homes. It is hot enough for a shower and a sink, cheap to keep, and it takes minutes rather than seconds to scald. The exception is a household where somebody has a weak immune system, where storing it hotter and mixing it down at the taps is the safer choice.

For most homes the answer is 120 degrees, and there is a good reason behind it rather than a guess.

At 120 the water is hot enough for a shower and the washing up, it costs less to keep hot, and it takes minutes of contact to cause a serious burn. At 140 that falls to a few seconds. The one case for going hotter is about bacteria, and it comes with a way to do it safely.

Before you start

What to carry: a kitchen thermometer and a glass. Ten minutes, then a few hours of waiting.

Gas or electric? A gas heater has one dial at the bottom, often marked with words or letters rather than numbers. An electric heater has two thermostats behind small panels on the side, one high and one low, and both need setting.

Measure before you change anything. The dial is a rough guide at best. What matters is the temperature at the tap, and the next section shows how to read it.

Three households where this matters more than money. Children and older people. Thinner skin burns faster and they are slower to pull away. In those homes, 120 at the tap is a ceiling, not a target.

Electric heaters: power off before the panels come off. The thermostats sit next to live terminals carrying 240 volts. Breaker off, then open the panels: how to reach and set both thermostats safely.

Never store water hotter without a mixing valve. If you set the tank higher for the reason in the fourth section, a thermostatic mixing valve at the heater brings it back down before it reaches a tap.

How to read what yours is really doing

Use the hot tap nearest the heater, let it run until the temperature stops climbing, then read it in a glass. That number is the one that matters, whatever the dial says.

Check 1Free, ten minutes

Measure it at the tap

Pick the hot tap closest to the heater. Taps further away read lower because the pipe has cooled the water on its way.

Run it for two or three minutes, until it stops getting hotter.

Fill a glass and put the thermometer straight in. Read it while it is still settling upwards and take the highest number.

Adjust in small steps. A gas dial moves a long way for a small mark. Move it a little, then wait three hours for the tank to settle before measuring again.

If it reads far hotter than the dial suggests, or it will not stop climbing, that is a thermostat problem rather than a setting: testing a thermostat that will not hold.

Why 120 is the usual answer

Roughly how long hot water takes to cause a serious burn on adult skin. Every step up the dial takes seconds off, and children burn faster than this.

Check 2

Weigh the burn risk and the bill

The burn risk climbs steeply. At 120 a serious burn takes minutes. At 130 it is around half a minute. At 140 it is a few seconds, and at 150 it is about a second and a half.

The bill falls as you turn it down. The US energy department puts it at three to five percent of your water heating cost for every ten degrees lower.

Dishwashers mostly heat their own water. Most modern ones have a heater inside, so they do not need a hotter tank. Check the manual if yours is old.

Going lower than 120 is where you stop saving and start running out of hot water in the shower, and it moves the tank towards the temperatures bacteria like.

When 140 is the better setting

Check 3

Store it hotter, deliver it cooler

The reason is Legionella, the bacteria behind a serious lung infection. It grows in warm water and is killed off at around 140. A tank held at 120 is not guaranteed to keep it down.

For most healthy households, 120 is still the normal advice and the risk is low.

For a household with somebody frail, elderly or immune suppressed, storing at 140 and fitting a thermostatic mixing valve at the heater gets both at once. The tank stays hot enough to kill bacteria, and the taps get water mixed down to a safe 120.

A tank that sits unused for weeks is also worth running hot for a few hours before use, then turning back down.

Already have a mixing valve? They wear, and a failing one sends water too hot or too cold to every tap: what a mixing valve fault looks like in the shower.

Holidays, tankless heaters and the odd cases

Check 4

The settings nobody explains

Going away. Most gas heaters have a Vacation setting that keeps the pilot and a little warmth. On an electric heater, switching off at the breaker for a week away is fine, and it must be switched back on with the tank full.

Tankless heaters are set on their own controller, usually in steps of a degree or two. The same 120 applies, and setting them hotter than you use just wastes gas: what else goes wrong with a tankless heater.

Water not hot enough even at the right setting is usually sediment, a failed element or the dip tube, not the dial: the order to check a heater that has gone lukewarm.

Water much too hot with the dial low is a thermostat stuck on, and it trips the safety cut out or lifts the relief valve. Treat it as a fault, not a setting.

Questions people ask

My gas heater has no numbers on the dial.

Most do not. Rheem’s manual puts the mark labelled Hot at about 125. Measure at the tap and adjust from there, because Rheem says the marks are only approximate.

Do both thermostats on an electric heater need the same setting?

Yes. Set them to the same number. A higher top thermostat does not give you more hot water, it only changes which element does the work.

Is 125 alright?

For most homes, yes. It is a sensible middle if 120 runs out too quickly in the shower, with the burn time still well over a minute.

The shower never gets as hot as the kitchen tap.

That is often the shower valve’s own anti scald stop, not the heater. It can be adjusted at the valve.

How long after changing it before I can measure?

Give it three hours, or run enough hot water to empty most of the tank and let it reheat. Measuring straight away only tells you what was already in there.

Does a lower setting make the tank last longer?

A little. Heat speeds up corrosion and scale, so a tank run at 120 tends to age more slowly than one kept hotter. The bigger lever on tank life is the anode rod: the rod that rusts so the tank does not.

Sources: Rheem use and care manual AP23698 (scald chart, dial marks, 120 degree starting point), the DOE Energy Saver Guide 2017 (120 degrees, dishwashers with their own heater), A.O. Smith "What Size Water Heater Is Right for You?" (120 recommended, mixing valves) and Whirlpool Energy Smart use and care guide 318686-001 (factory setting, mixing valve)