120 degrees Fahrenheit is the safety recommendation against scalding, but 140° is the common default setting. Most experts agree that anything below 120 degrees creates a risk for bacteria to develop inside your water heater from stagnant water, such as legionella that causes Legionnaire's disease.
B - 140° F - Less than 5 seconds. A - 130° F - About 30 seconds. HOT - 120° F - More than 5 minutes.
In the US, the maximum legal temperature for a water heater in a residential setting is 120 degrees. Most folks want to run at 125-130 degrees but be careful. The Federal law that stipulates the max temperature is because of folks, especially kids, getting burned by the water.
The recommended setting for this control is 60°C/140°F. (Storing hot water at temperatures of less than 55°C is not advisable due to potential for Legionnaires disease). If the water coming out of your taps is too hot then check this control as it could be set too high.
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.
Water Heater Temperature Recommendations
120 degrees Fahrenheit is the safety recommendation against scalding, but 140° is the common default setting.
Hot water needs to be stored above 60°C in hot water systems to prevent bacteria growth (such as Legionella), but a tempering valve ensures that the water comes out of the tap at a lower temperature.
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.
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.
Adjust both thermostats to the same temperature setting. WARNING! Higher temperatures increase the risk of scalding. If you have increased the temperature setting above 120°F, install Thermostatic Mixing Valves at each point of use and set them to 120°F or lower.
Turning up the heat at the water heater causes hotter water to go to the hot tap. If you desire the same temperature, this makes you use more of the cold tap. Therefore, you're using a smaller percentage of hot water for the same total shower flow. This makes the perceived hot water in your tank last longer.
These are usually labeled A, B, C or 1, 2, 3, and the last setting is always “Very Hot.” The A or 1 setting should be around 130 degrees, B or 2 is 140 degrees, C or 3 is 150 degrees and “Very Hot” is always 160 degrees. Again, we never recommend setting the unit above the B or 2 setting to prevent scalding.
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.
The next highest setting is usually either labeled as “Hot” or with a triangle, and this setting should correspond to 120 degrees. From there, you will typically see three higher settings marked either as 1, 2, and 3 or A, B, and C that correspond to 130, 140, and 150 degrees, respectively.
The primary way most people notice their water heaters overheating is because the water becomes unbearably hot, scaldingly so. If your water heater is set on too high a temperature, burns, and severe injuries may occur.
The perfect temperature to set a water heater
If you're looking for a short answer, it's 120 degrees Fahrenheit (about 49 degrees Celsius).
If your shower is not heating up, there's likely an issue with your water heater. It could be overworked and need time to regenerate. However, there may be other complications. Sometimes, your shower may stay warm for a short time until it suddenly turns cold.
While there are chillers that can produce hotter water, for practical purposes the heating hot water temperature should be limited to no more than 140°F for standard machines using standard refrigerants. Even lower temperatures are desirable when possible.
General Recommended Water Heater Temperature
If you go to the Environmental Protection Agency, you'll receive a recommended water temperature of 120 degrees Fahrenheit.
Try heating the water for an hour in the morning and an hour in the evening. Start the water heating about an hour before you need it. For example, if you shower at 08:30, start heating the water at 07:30. If you wash up in the evening at 19:30, then start the water heating at 18:30.
It's generally much cheaper to heat water using your central heating system, rather than using electricity with an immersion. The exception might be during the summer, when you have your central heating turned off, or if you have an old inefficient boiler.