How to Adjust the Temperature on Water Heaters

Step-by-step guide on how to adjust the temperature on water heaters. Learn about the safe or optimal temperature settings, dealing with the thermostats on gas and electric models to protect yourself from scalding hot water and avoid failure.

What is the safe temperature?

Every gas and electric water heaters are equipped with the adjustable manual thermostat which allows you to control the water temperature in the tank and faucet.

Water heater is built to produce hot water in the temperature range from approximately 80 F to 160 F or higher when used in commercial applications. The water heaters are shipped with the thermostats factory set on 120-125 F, which is considered as "safe" or optimal. Keep in mind that different temperature settings are used for bath or shower (120 F) and laundry or dish-washing (120-140 F). The following shows the approximately time-burn relationship for the adult skin:

  • 120 F - more than 5 minutes

  • 125 F - 2 minutes

  • 130 F - 30 seconds

  • 140 F - less than 5 seconds

  • 150 F - 1.5 seconds before the burn occurs.

Depending on the time and person's age, scalding may occur at different hot water temperatures. Kids and elderly are especially susceptible to burns, so they should be protected by decreasing the temperature on the thermostat or by installing the mixing valves (temperature limiting valves). These anti-scald devices are very useful as they reduce the temperature at the point of use, by mixing the cold and hot water to the desired temperature.

Lower temperatures are recommended for one home, as they are safe and provide an energy-efficient operation, but if the temperature is too low, the tank will run out of hot water fast or even worse, the bacteria will develop inside the tank.

Adjusting the temperature on electric water heaters

water heater thermostat with eco


emergency plumber

Follow these steps when adjusting the temperature on electric water heaters:

  • Before you do any adjustments, measure the temperature of hot water at the tap. The goal is to adjust the temp. to approximately 120 F or whatever you require.
  • Turn the electricity OFF to the heater. Do not try to adjust the temperature with the power ON.

  • In order to access the thermostats, both lower and upper one, remove the access panels and foam insulation that covers the thermostats.

  • Use the flat screw driver and rotate the adjusting knob to the desired temperature.

  • Put the access panel and the foam back and resume the power.

  • Wait for a few hours for the hot water in the tank to stabilize and measure the temperature at the faucet. If 120 F is the goal, mark the setting on the thermostat with the marker.

Adjusting the temperature on gas water heaters

robertshaw gas control valve and thermostat

Adjusting the temperature on gas water heaters is simpler than on electric units, since it doesn't require any tools and is easily accessible. The thermostat is part of the gas control valve and is located at the bottom of the heater. White Rodgers, Honeywell and Robertshaw are the most used. The thermostat dials on all gas control valves are set to its lowest temperature setting when shipped to you.

In order to increase the temperature on water heaters with the WR valves, you should turn the dial counterclockwise while on Robertshaw and Honeywell valves is opposite, clockwise to increase, counterclockwise to decrease. Most of the temperature dials are marked with the " Warm" (120 F) and "Hot" (160 F) and have the "optimal temperature" (130 F) mark. Some of the gas valves, such as Honeywell have the "Vacation" mode (85 F) to adjust the temperature when the water heater is not in use for the long period of time.

If the temperature of the hot water exceeds the maximum allowed (usually 180 F) and to prevent overheating, a high-temperature limit switch or ECO (part of the gas control valve) activates, shutting down the whole unit.

Lower thermostat settings on water heaters are OK during low demand periods as long as it satisfies your needs or during the absence, as it will reduce the energy loss and prevent the tank from freezing during cold weather. Turning the water heater temperature down also means reduced scale sediments and less corossion.

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