How to Adjust the Temperature on Water Heaters

A step-by-step guide on how to adjust the temperature on tank-type water heaters. Learn about the safe and optimal temperature settings, how properly to operate the thermostat on both gas and electric models, protect you and your family from scalding hot water, and avoid element failure.

The main reasons why hot water coming from the water heater have to be appropriately regulated and kept at the recommended temperature, are to avoid scalding burns and high energy bills.

Did you know that according to the American Burn Association, approximately 21,000 of children get injuries from the hot water tap?

What is the safe temperature?

Every gas and electric water heaters are equipped with the adjustable manual thermostat so the user can control and regulate the water temperature inside the tank.

The water heater is built to produce hot water with the temperature ranging from approximately 80 F to 160 F, or higher when used in commercial applications. Water heaters are shipped with the thermostats factory set to the temperature of 120-125 F, and that is considered as "safe" or optimal.

Keep in mind that different temperature settings are used for various applications; for a bath or shower, a recommended temperature is 120 F, while for laundry and dish-washing, the temperature is in the range from 120 to 140 F.

The following shows the relationship between the temperature and exposure time that can produce burns on the adult body:

  • 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 exposure time and person's age, scalding burns may occur at different temperatures of hot water. Kids and elderly are especially susceptible to burns, so they should be protected by decreasing or correcting the temperature on the thermostat, or by installing the mixing valves (temperature limiting valves).

These anti-scald devices are handy as they reduce the temperature at the point of use, by mixing the cold and hot water to the desired temperature. Some plumbing codes and manufacturers could require the installation of such valves.

Lower temperatures are recommended for residential homes, 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 (Legionella) will develop inside the tank.

Legionella is commonly found in potable water sources such as hot tubs, showers, swimming pools and so on. It takes half an hour for Legionella to die when exposed to a temperature of 140 F, while the safe range is from 158 F. By using the mixing valve, you can still keep the temperature on the thermostat at the higher level, but deliver it at safe temperatures at the point of use.

Problems

If the water coming out from the water heater is too hot and cannot be regulated, most likely there is a problem with the thermostat. In the electric water heaters, there is a red reset button which triggers if the thermostat fails to shut off the power to the heating element. If there is a problem with both thermostat and reset button, the heating element will continue to draw the power and heat the water to unsafe levels. You can even see the steam coming out the TPR valve, or hear boiling inside the tank.

If the temperature exceeds the safe level, the temperature and pressure relief valve (TPR) will open, and water will be dripping.

Excessive sediment buildup on the heating elements can make them work hard, corrode, overheat and eventually burn out.

Call a professional plumber if you have a problem with hot water and to avoid further more series problems.

Adjusting the temperature on electric water heaters

Electric thermostatElectric thermostat

Follow these steps when changing the temperature of hot water on electric water heaters:

Before you make any adjustments, measure the temperature of hot water at the tap. The goal is to adjust the temperature to approximately 120 F.

  • Turn OFF the electricity to the heater. Do not try to regulate 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 screwdriver and rotate an adjusting knob to the desired temperature.
  • Once the thermostat is set to desired temperature, put the access panel and foam back and resume the power.
  • Wait for a few hours, so the temperature of hot water inside the tank stabilizes, and measure the temperature at the faucet. If the temperature of 120 F is your goal, mark the setting on the thermostat with the marker.

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Adjusting the temperature on gas water heaters

Robertshaw gas valveRobertshaw gas valve

Regulating the temperature on gas water heaters is more straightforward than on electric units, since it doesn't require any tools, and access to the thermostat is straightforward.

The thermostat is part of the gas control valve that is located at the bottom of the heater. Almost all of the manufacturers of water heaters use gas valves made by one of the following companies; White Rodgers, Honeywell, and Robert Shaw.

The thermostats on the gas valves are usually set to its lowest temperature setting.

To increase the temperature on water heaters with the White Rodgers 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 an extended period.

If the temperature of the hot water exceeds the maximum allowed (usually 180 F) and to prevent the 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 the periods of low demand and 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 corrosion.

Note: It is useful to know that if you reduce the temperature by 10 degrees F, you could get between 3 and 5% just in energy savings.

Conclusion

The best setting could vary from one user to another. However, if we want to follow an expert advice, such as the U.S. Environmental Protection Agency (EPA), the temperature of 120 F will keep the bacteria away, and water won’t be too hot to cause scalding. Also, with the higher temperatures of water, the minerals will deposit faster, and the energy bill will be higher.

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