How to Check and Set Your Water Heater Temperature
Your water heater temperature affects safety, energy bills, and appliance longevity. Most water heaters ship from the factory at 140°F — high enough to cause third-degree burns in under 5 seconds. The recommended setting of 120°F prevents scalding, kills harmful bacteria, and can save you up to $60 per year on energy costs.
Time Required
5-10 minutes (plus wait time)
Difficulty
Easy
Tools Needed
Thermometer, screwdriver (electric)
Scald Safety Warning
Water at 140°F causes third-degree burns in just 5 seconds. At 150°F, it takes only 1.5 seconds. Children and elderly adults have thinner skin and are at even greater risk. If your water heater is set above 120°F, exercise extreme caution when testing water temperature and always test with a thermometer before putting hands under the stream.
Test Your Current Water Temperature
Before adjusting anything, measure what your water heater is actually delivering. The dial setting and the actual faucet temperature can differ by 10-20 degrees.
Choose the nearest hot water faucet
Use the faucet closest to your water heater for the most accurate reading. The further away the faucet, the more heat is lost in the pipes. A kitchen or bathroom sink near the water heater works perfectly.
Run hot water for 2 full minutes
Turn the hot water on full and let it run until it reaches maximum temperature. This purges the cooler water sitting in the pipes and gives you a reading of what the tank is actually producing.
Measure with a thermometer
Hold a cooking thermometer, instant-read meat thermometer, or candy thermometer directly in the hot water stream. Wait for the reading to stabilize. Record the temperature. If it's above 120°F, you should lower it.
Adjusting a Gas Water Heater
Find the gas control valve
The temperature dial is on the front of the gas control valve, usually near the bottom of the tank. It's a round knob with temperature markings or letter grades. No tools are needed — you turn it by hand.
Understand the dial markings
Many gas heaters don't show exact temperatures. Look for a triangle symbol or the letter "A" — this is typically around 120°F. "Warm" is usually 90-110°F, "Hot" is about 140°F, and "Very Hot" can be 150-160°F. When in doubt, set it to the triangle mark and verify with your thermometer.
Wait 2-3 hours and retest
After adjusting the dial, wait at least 2 hours for the entire tank to reach the new temperature. Then run the faucet test again. Small adjustments are better — if you overshoot, you'll have to wait another 2 hours to test again.
Adjusting an Electric Water Heater
Turn off the breaker
Electric water heaters run on 240 volts — enough to be fatal. Before opening any access panels, flip the breaker labeled "Water Heater" at your electrical panel to the OFF position. Verify power is off by checking that the indicator light on the heater (if present) is dark.
Remove the access panels
Most electric water heaters have two access panels (upper and lower) on the side, secured with screws. Remove both panels and peel back any insulation to reveal the thermostats. Each thermostat has a temperature dial you adjust with a flathead screwdriver.
Adjust both thermostats to the same setting
Use a flathead screwdriver to turn both the upper and lower thermostats to 120°F. Both should match — if one is set higher than the other, you'll get inconsistent temperatures. Replace the insulation and panels, then restore power at the breaker.
Why 120°F Is the Sweet Spot
- Scald prevention: At 120°F, it takes over 5 minutes of sustained contact to cause a burn. At 140°F, it takes only 5 seconds. This difference is critical in households with young children or elderly family members.
- Bacteria control: 120°F is hot enough to prevent Legionella bacteria growth in the tank. The bacteria that causes Legionnaires' disease thrives between 77-113°F and is killed above 122°F.
- Energy savings: Every 10°F reduction saves 3-5% on water heating costs. Dropping from 140°F to 120°F saves $36-$61 per year on average.
- Reduced mineral buildup: Higher temperatures accelerate mineral deposit formation inside the tank and pipes. Keeping the temperature at 120°F slows sediment buildup and extends tank life.
Pro Tips
- •Mark the dial position: After finding the perfect setting, use a permanent marker to draw a line on the dial and the housing. If someone accidentally bumps the dial, you can return it to the exact position without re-testing.
- •Test at multiple faucets: Check the temperature at both near and far fixtures. If the far faucet is significantly cooler, your pipes may benefit from insulation, or you may need a recirculation system for long pipe runs.
- •Consider a thermostatic mixing valve: If someone in your household needs water above 120°F (for a medical condition or dishwasher without a booster heater), install a thermostatic mixing valve. It lets you set the tank to 140°F while delivering 120°F at faucets, blending hot and cold water automatically.
- •Vacation mode saves money: If you'll be away for more than a few days, turn the water heater to its lowest setting or "Vacation" mode. There's no reason to keep 40-80 gallons of water hot when nobody is using it.
Frequently Asked Questions
What temperature should my water heater be set to?
The U.S. Department of Energy recommends 120°F (49°C) for most households. This temperature prevents scalding, kills most bacteria, and saves energy compared to higher settings. If anyone in the household is immunocompromised, some guidelines suggest 140°F, but a thermostatic mixing valve should be installed to prevent scalding.
How much money can I save by lowering my water heater temperature?
Lowering your water heater from 140°F to 120°F can save $36-$61 per year in energy costs according to the U.S. Department of Energy. It also reduces standby heat loss from the tank and slows mineral buildup and corrosion, which can extend the life of your water heater and pipes.
Why doesn't my water heater have specific temperature numbers on the dial?
Many gas water heaters use vague labels like "Warm," "Hot," and "Very Hot" instead of specific temperatures. This is because the actual water temperature depends on factors like incoming water temperature, tank size, and demand. The triangle or "A" mark is usually around 120°F. Always verify with a thermometer at the faucet rather than trusting the dial markings.