How to Adjust Water Temperature
Updated February 20, 2026
Set your gas or electric water heater thermostat to the right temperature for comfort, safety, and lower energy bills -- plus how to verify the actual output with a thermometer.
Overview
Most water heaters ship from the factory set to 140 degrees F. That is way too hot for most homes -- it wastes energy, and water at 140 degrees can cause a third-degree burn in under 5 seconds. The sweet spot is 120 degrees F. It is comfortable for showers and daily use, safe for everyone in the household, and dropping from 140 to 120 saves 6-10% on your water heating bill. On a gas unit, the adjustment takes about 2 minutes -- you are just turning a dial. Electric units take 5 minutes because you need to pull an access panel. Either way, this is about as simple as it gets.
What You'll Need
Safety First
- Electric water heaters: kill the breaker before you pull the access panel. There is 240 volts behind that cover. Use a non-contact voltage tester to confirm power is off before you touch anything.
- Never set it below 120 degrees F. Below that temperature, Legionella bacteria can grow in the tank -- the bacteria that cause Legionnaires' disease. 120 is the floor for safe potable water storage.
- After adjusting, test the water at a faucet with a thermometer before anyone bathes. This is critical in homes with young kids, elderly family members, or anyone who may not react quickly to scalding water.
Step-by-Step Instructions
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Adjust a Gas Water Heater Thermostat
On a gas unit, the thermostat dial is on the gas control valve at the bottom front of the tank. You will see labels like HOT, WARM, and LOW (or A, B, C), plus a vacation or pilot setting. Some have degree markings. Just turn the dial -- for 120 degrees, set it to WARM or the mark between LOW and HOT. No covers to remove, no power to shut off. Wait 2-3 hours for the tank to reach the new temperature, then test at a faucet.
Tip: Fair warning -- gas water heater dials are notoriously imprecise. The actual water temp can be 10-20 degrees off from the dial setting. Always verify with a thermometer. You may need to nudge the dial a bit higher or lower to actually land on 120. -
Adjust an Electric Water Heater Thermostat
Electric units have one or two thermostats behind metal access panels on the side of the tank. Kill the breaker first. Remove the panel screws, set the panel aside, and peel back the insulation to expose the thermostat. You will see a temperature adjustment screw -- use a flathead screwdriver to turn it. Clockwise increases the temp, counterclockwise decreases it. If there are two thermostats (upper and lower), set both to the same temperature. Put the insulation back, reinstall the panel, flip the breaker on, and wait 2-3 hours before testing.
Tip: Two thermostats? Set them both the same. If the upper is set higher than the lower, the top of the tank runs hotter than the bottom and you get inconsistent temps at the faucet. -
Verify the Actual Water Temperature
After 2-3 hours, test the actual water temperature at the faucet closest to the water heater. Run the hot water for 60 seconds to flush the cooler water sitting in the pipe, then hold a cooking thermometer or instant-read thermometer under the stream. You are looking for a reading within 5 degrees of your target. Too hot or too cold? Adjust the thermostat slightly and wait another 2-3 hours before retesting.
Tip: Always test at the closest faucet for the most accurate reading. Water loses heat as it travels through pipes -- a faucet 50 feet away through uninsulated pipes might read 110-115 even if the tank is putting out 120. Pipe insulation cuts that heat loss significantly. -
Consider Special Situations
A few situations where 120 might not be enough: older dishwashers without a built-in heater may need 140 for proper sanitizing, though most modern dishwashers handle 120 just fine with their internal heaters. If hot water runs out fast at 120, the problem is tank capacity, not temperature -- cranking the dial up is a band-aid that wastes energy. Look into a larger tank or a tankless unit instead. And if you notice reduced flow at the hot faucet after lowering the temp, sediment in the tank may be the culprit -- flushing the tank usually clears that up.
Tip: Going on vacation? Set the thermostat to the lowest setting or VACATION/PILOT mode. No sense heating a full tank of water that nobody is using. You will save $5-10 per week. Just remember to turn it back up when you get home -- it takes 1-2 hours to reheat.
Pro Tips
- 120 degrees is the number recommended by the Department of Energy and the number we recommend. It prevents bacterial growth, minimizes scalding risk, and saves energy. Unless you have a specific reason to run hotter, 120 is the right answer.
- Every 10-degree drop saves 3-5% on water heating costs. Going from 140 to 120 saves $30-60 per year for a typical household. That is real money for turning a dial.
- If scalding is a concern -- especially with young kids or elderly family members -- install thermostatic mixing valves at individual faucets or showerheads. They are $15-30 each and physically limit the output temperature by mixing in cold water. An extra layer of safety beyond the water heater thermostat.
- Got a tankless water heater? Adjust the temp on the digital control panel instead. Tankless units are much more precise than tank-style thermostats -- they hold the set temperature within 1-2 degrees. Same 120-degree recommendation applies.
- If the thermostat is set to 120 but the water at the tap is hitting 130+, the thermostat is probably failing. That is a safety issue. Get it replaced sooner rather than later.
When to Call a Pro
The adjustment itself is as simple as it gets -- no pro needed. But call a plumber if the thermostat seems to be malfunctioning (water is way hotter or colder than the setting), if you cannot access the thermostat on an electric unit (corroded screws, sealed panels), or if you want a whole-house thermostatic mixing valve installed for scalding protection.