The best temperature setting for a hot water heater is between 120 and 140 degrees. Below 120 degrees, bacteria can develop in the stagnant water sitting in the tank. Above 140 degrees, the water is so hot that you and your family members can be at risk for scalding in as little as two seconds.
The maximum Department of Energy recommended water heater temperature setting you should never exceed is 140 degrees Fahrenheit. The lowest recommended setting should never be below 120 degrees Fahrenheit.
According to Centers for Disease Control and Prevention (CDC), water temperatures ranging from 130 to 140 degrees Fahrenheit(°F) can eliminate most of the harmful bacteria. However, be warned that these high temperatures can also increase the risk of scalding.
The U.S. Consumer Product Safety Commission (CPSC) urges all users to lower their water heaters to 120 degrees Fahrenheit. In addition to preventing accidents, this decrease in temperature will conserve energy and save money. Most adults will suffer third-degree burns if exposed to 150 degree water for two seconds.
Water Heater Temperature Recommendations
120 degrees Fahrenheit is the safety recommendation against scalding, but 140° is the common default setting.
To help prevent bacteria growth, the ASSE recommends keeping the water in your water heater tank at about 135 - 140 degrees Fahrenheit.
Manufacturers often recommend a hot water heater temperature between 120 to 140°F, and there's a reason for this. The Occupational Safety and Health Administration (OSHA) recommends a recommended hot water temperature of at least 122 degrees to prevent the growth of harmful bacteria.
Although some manufacturers set water heater thermostats at 140ºF, most households usually only require them to be set at 120ºF, which also slows mineral buildup and corrosion in your water heater and pipes. Water heated at 140ºF also poses a safety hazard—scalding.
Cold shock can be just as severe and dangerous from water temperatures of 50-60F (10-15C) as it is from water at 35F (2C). Gasping for a breath or rapid breathing from sudden immersion can be triggered by water as warm as 77F (25C).
The EPA recommends 120 degrees because it's hot enough to keep diseases at bay but not hot enough to cause scalding. This setting will also supply enough hot water for most small families and is relatively energy efficient.
Raising the temperature setting on your water heater ultimately makes your hot water supply last longer. It will ensure everyone gets a hot shower, with plenty leftover to run your dishwasher and washing machine.
If the temperature is above 65°C, then the water will be too hot to use, and it increases the risk of serious burns. Keeping the temperature at a safe level, 60°C to 65°C, makes the water hot enough to use and hot enough to kill unwanted bacteria.
There were two temperatures discussed for each fixture during the design standard meetings. One was the “use temperature” and the other was “the maximum temperature” to prevent scalding. It's generally agreed that 120 degrees Fahrenheit is the maximum safe hot water temperature that should be delivered from a fixture.
Mineral Build-Up
Mineral build-up on the heating element of a hot water tank can cause a water heater to overheat. If your water heater's element overheats, it's logical that your water will come out of the faucet way too hot.
At 150 degrees, which is definitely way too hot, it takes only seconds for the water to cause third-degree burns. This is why a water heater temperature of 150 degrees is especially hazardous in residences with children or the elderly.
Different recommendations on water temperature may confuse you a bit. But if you keep your hot water temperature at 120 degrees to 140 degrees Fahrenheit, you'll be within an acceptable and safe range. You also need to provide scheduled monitoring of your faucet water to gauge its temperature.
The best temperature range for water to be absorbed and rehydrate effectively is between 10-22 degrees Celsius (50 - 72 degrees Fahrenheit).
Human exposure to hot water at 140°F can lead to a serious burn within 3 seconds, whereas at 120°F a serious burn takes about 10 minutes. Because thinner skin burns more quickly, children and older adults are at increased risk.
Safety and Comfort
According to the American Red Cross the recommended water temperature ranges from 78°F to 85°F for the most comfortable and safe swimming experience, but it can vary depending on who is using the pool, and for what purpose.
Most homeowners should flush their water heaters every 6 months or so, but if you have extremely hard water, you may want to do it more often. Flushing your hot water heater could be necessary as often as every few months depending on the mineral content of your local water supply.
120 Degrees is the recommended max temperature for water heaters, according to both the American Society of Sanitary Engineering and the US Department of Energy. Firstly, setting the max temperature to 120 degrees prevents the water from scalding your skin.
It takes only 32 minutes on average for Legionella to die at temperatures of 140 degrees, and at 151 degrees, the bacteria will die instantly. This is why disinfection that uses temperature change will set a water heater to approximately 158 degrees for five minutes.
Making sure your water heater is always set to at least 120 degrees minimizes this risk, as the water should be hot enough to kill any bacteria. Even though most units will go up to 160 degrees, you really shouldn't ever set the temperature higher than 140 degrees in order to reduce the risk of scalding.
According to most dermatologists, the ideal shower temperature is anywhere between 98°F (37°C) and 104°F (40°C)—and no more than 105 °F (41°C). Rinsing under lukewarm water allows you to stay comfortable and maintain your body temperature while reaping all the benefits of both hot and cold showers.
Overheating water heaters sometimes cause corrosion in the tank. This corrosion can cause leaks and other issues.