What Temperature Should a Water Heater Be Set To?
Updated 2026-08-16 · 5 min read
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There's a genuine tension in this question, and most advice picks a side without saying so.
Temperature trade-offs
| Setting | Scald risk | Legionella risk | Energy |
|---|---|---|---|
| 120°F | Low | Present below ~120°F | Lowest — the common recommendation |
| 130°F | Moderate | Reduced | Middle |
| 140°F | High — seconds to burn | Suppressed | Highest standby loss |
120°F is the widely recommended residential setting: hot enough for normal use, low enough that a child or older adult is not scalded in seconds. Households with immune-compromised occupants sometimes store hotter and fit a thermostatic mixing valve at the outlet — storing at 140°F while delivering 120°F, which addresses both risks at once.
What are the risks of the wrong water heater temperature?
Scalding. Hot water causes burns quickly, and the time to injury falls sharply as temperature rises. At around 140°F a serious burn can occur in seconds; at 120°F it takes far longer, giving time to react. Children, older adults, and anyone with reduced sensation or mobility are at greatest risk.
Legionella. Legionella bacteria can grow in warm water. Growth is favored in a range roughly spanning the low 70s to well over 100°F, and higher temperatures suppress it. Water heaters kept at low temperatures — particularly large tanks with low turnover, or systems in homes left unoccupied — are the concern.
These pull in opposite directions, which is why guidance differs.
What temperature should a water heater be set to?
120°F is the most widely cited setting for households. It is:
- Hot enough for showering, dishwashing, and laundry
- Substantially safer against scalds than higher settings
- Lower in standby losses, so slightly cheaper to run
Many manufacturers ship units set around 120–125°F for this reason.
Should you store water hotter than 120°F?
Where Legionella risk is a greater concern — large tanks, low usage, long pipe runs, occupants with compromised immunity — the recommendation shifts toward storing at 140°F.
The resolution isn't to accept scald risk. It's a thermostatic mixing valve installed at the heater outlet, which blends hot storage water with cold to deliver a safe temperature at the taps.
That gives you both: hot storage that suppresses bacterial growth, and moderate delivery temperature that won't scald.
It's an inexpensive device and it's the standard answer to this trade-off. If you have reason to store hot, install one rather than choosing between the two risks.
Dishwashers
Older dishwashers relied on incoming water being hot. Most modern ones have internal heating elements and will raise the temperature themselves, so a 120°F supply is generally fine.
Check your dishwasher's manual if you're unsure — a small number still specify a higher inlet temperature.
How do you change a water heater temperature?
Gas: a dial on the thermostat at the front of the tank, often marked with settings rather than numbers. Turn it, wait a few hours, and measure.
Electric: thermostats behind access panels — usually two, upper and lower, and both must be set to the same value or the unit behaves oddly.
Turn off the breaker first. The terminals behind those panels are energized at 240 volts. This is not optional. See how to reset a tripped breaker for panel basics.
Then measure. Run hot water at the nearest tap for a couple of minutes and check with a thermometer. Dial markings are frequently inaccurate, and what matters is the delivered temperature, not the label.
How much does lowering the temperature save?
Lowering the setting reduces standby losses and the energy per gallon heated. The saving is real but modest — this is a sensible adjustment rather than a transformative one.
Larger levers on water heating cost:
- A heat pump water heater, which cuts energy use to roughly a third — see heat pump water heaters explained
- Fixing leaks. A dripping hot tap wastes heated water continuously
- Insulating hot water pipes, especially the first several feet from the tank
- Lower-flow fixtures
- Setting back while away — most units have a vacation mode
See cost to run a water heater.
If you have young children
Beyond the tank setting, consider:
- A thermostatic mixing valve at the heater, or at individual fixtures
- Anti-scald valves in showers and tubs, which are required in new construction in many jurisdictions
- Supervision, which is the real control regardless of settings
What are the signs the temperature is set wrong?
Too low: hot water that runs lukewarm quickly, dishes not cleaning well, or a persistent musty smell from the hot tap — which can indicate bacterial growth and is worth acting on.
Too high: water that's uncomfortable at full hot, visible steam at the tap, or a pressure relief valve discharging.
If water is never hot enough regardless of the setting, that's a fault rather than a setting — see water heater not heating: troubleshooting.
Standards and code reference
The standards behind this guide, for looking up in the edition your jurisdiction has adopted:
- ASSE 1017 / ASSE 1070 — thermostatic mixing valve standards, for storing hot and delivering safe
Code editions and local amendments vary. Confirm the adopted edition with your AHJ, and treat manufacturer instructions as governing wherever they are more restrictive.
Where to go next
More in our heating and cooling guides.
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