Most water heaters should be set to 120°F (49°C) for a safe balance between scald prevention and energy savings, though 140°F (60°C) is worth considering if you’re concerned about bacterial growth. The right temperature for your household depends on who lives there and how you use hot water. Adjusting the setting takes just a few minutes on a gas heater and slightly longer on an electric one.
What Temperature to Choose
The U.S. Department of Energy recommends 120°F as a baseline for most homes. At this temperature, water takes about four minutes of sustained contact to cause a scald burn, which gives you a reasonable safety margin during showers and handwashing. By contrast, water at 140°F scalds in just one second, and 150°F water scalds in less than a second. If you have young children or elderly household members with reduced skin sensitivity, 120°F is the safer choice.
There’s a tradeoff, though. Legionella, the bacterium that causes Legionnaires’ disease, can multiply inside a water heater tank set to 120°F. Setting the thermostat to 140°F effectively kills Legionella but reintroduces the scald risk at every faucet. A practical compromise: set the heater to 140°F and install anti-scald mixing valves or thermostatic valves at your showerheads and bath faucets. These blend cold water in at the tap so the delivered temperature stays at or below 120°F while the tank stays hot enough to suppress bacteria.
Households with immunocompromised members or those on well water have more reason to lean toward the higher setting. If everyone in the home is healthy and mobile, 120°F is usually fine.
Dishwashers and Other Appliances
Your dishwasher needs incoming water of at least 120°F to clean effectively and dissolve grease. GE recommends water between 120°F and 150°F for proper performance. Most modern dishwashers have an internal booster heater that bumps the temperature up for the sanitize cycle, but they can’t heat cold water from scratch. If your water heater is set below 120°F, your dishes may come out greasy or poorly sanitized. Washing machines set to “hot” also pull directly from the tank, so going below 120°F can reduce cleaning power there as well.
How to Adjust a Gas Water Heater
Gas water heaters make this easy. The thermostat is built into the gas control valve, a box-shaped unit near the bottom of the tank with a visible dial or knob on its face. No tools required, and you don’t need to shut anything off first.
- Find the dial. Look at the front of the gas control valve, near the bottom of the unit. It typically has marked temperatures or labels like “Low,” “Medium,” “Hot,” and sometimes a triangle or notch indicating the recommended setting.
- Turn to your preferred temperature. If the dial shows numeric temperatures, rotate it to 120°F (or 140°F if you’re using anti-scald valves). If it only shows labels, “Medium” or the triangle mark usually corresponds to roughly 120°F, but check your owner’s manual to confirm.
- Verify the pilot light. Make sure the status light on the gas control valve is flashing about once every three seconds, which indicates normal operation.
- Wait and test. Give the heater one to two hours to reach the new temperature before testing at a faucet.
How to Adjust an Electric Water Heater
Electric heaters require more caution because the thermostats sit behind access panels on a live electrical appliance. The adjustment itself is simple, but you need to cut power first.
- Turn off the breaker. Find the circuit breaker for your water heater in your electrical panel and flip it to the OFF position. This is not optional. Working on an energized electric water heater can cause electrocution.
- Confirm the power is off. Open the electrical junction box on top of the water heater and use a non-contact voltage tester on the wires. If you don’t own one, they cost under $20 at any hardware store and are worth having.
- Remove the access panels. Most electric heaters have two panels, one upper and one lower, each held in place by a couple of screws. Behind each panel you’ll find insulation. Fold it out of the way to expose the thermostat.
- Adjust with a flathead screwdriver. Each thermostat has a small dial or screw with temperature markings. Turn it clockwise to increase the temperature and counterclockwise to decrease it. Set both thermostats to the same temperature. If the upper thermostat is set higher than the lower one, you may run out of usable hot water faster.
- Reassemble and restore power. Fold the insulation back, screw the access panels on securely, close the junction box cover, and flip the breaker back on.
Electric heaters may take two to three hours to fully reach the new set point, so wait before testing.
How to Check the Actual Temperature
The number on the dial is not always what comes out of your faucet. Sediment buildup, long pipe runs, and aging thermostats can all create a gap between the setting and reality. The only way to know your actual delivery temperature is to measure it.
Go to the hot water faucet that’s farthest from your water heater. Turn on the hot side only and let it run for about a minute so you’re getting fully heated water, not the cooled water sitting in the pipes. Hold a kitchen thermometer or a meat thermometer in the stream for at least 60 seconds, then read the temperature. If it’s significantly off from your target, go back and nudge the thermostat up or down, wait an hour or two, and test again.
This is also a useful check if your water suddenly feels less hot than it used to. A heater with heavy sediment at the bottom can fool the thermostat into reading the temperature of the mineral buildup rather than the water itself. The thermostat thinks the tank is up to temperature and shuts off the burner or element early, leaving you with lukewarm water. If you notice this pattern, the tank likely needs to be flushed.
Sediment and Thermostat Accuracy
Minerals in your water supply settle to the bottom of the tank over time, forming a layer of calcium and sedite that insulates the water from the heating element (in electric models) or burner flame (in gas models). This forces the heater to work harder and longer, raising energy costs. In severe cases, the sediment coats the thermostat sensor directly, causing it to misread the water temperature by 10°F or more.
Flushing the tank once a year prevents this. You connect a garden hose to the drain valve at the bottom of the heater, open the valve, and let water flow out until it runs clear. On a tank that hasn’t been flushed in years, you may see sandy, gritty, or rust-colored water. Clearing out that sediment restores heating efficiency, improves thermostat accuracy, and can noticeably increase the amount of hot water your tank delivers per cycle. If your heater makes popping or rumbling noises when it fires up, that’s the sound of water boiling beneath a layer of sediment, a clear sign it’s overdue for a flush.
Signs Your Setting Needs Adjusting
A few common situations suggest it’s time to revisit your thermostat. If your hot water runs out faster than it used to, sediment or a drifting thermostat could be the culprit. If you or your family members are getting surprised by scalding water, the setting may be too high or may have been bumped accidentally. If your energy bill has crept up without other explanation, lowering from 140°F to 120°F can cut water heating costs by 6 to 10 percent. And if you’ve recently added a household member, especially a baby or someone with limited mobility, it’s worth double-checking both the tank setting and the temperature at your most-used faucets.