How Hot Should a Water Heater Be?

The proper temperature setting for a water heater is a hotly debated topic. Savvy homeowners know that heating water – and maintaining it at an elevated temperature – is a large part of any home energy budget. Some people reduce the temperature in the firm belief that heating water to lower temperatures requires less energy and therefore results in energy savings. Other homeowners take the opposite stance and reason that hotter water can be mixed with greater volumes of cold water to reach a desired temperature and so actually saves money by resulting in less usage.

Both of these answers are correct, in their own way, and both are also incorrect. Here’s why.

Hot Water is Dangerous

Most people don’t realize how dangerous hot water can be. Any modern water heater can produce water hot enough to instantly cause first degree burns and produce second degree burns within one second. Hot water tanks even have warning stickers advising that temperatures of 125 Fahrenheit or greater can cause burns or death.

Despite the warnings, homeowners often crank up the water heater to dangerous settings. With the proper safety devices installed, higher temperatures are OK, but most homeowners do it for the wrong reason and fail to install necessary safety devices.

In March 2012, the American Society of Sanitary Engineering’s Scald Awareness Task Group published the “Understanding Potential Water Heater Scald Hazards” white paper. That publication focused on water heater settings and the general misconceptions that homeowners have regarding those settings. For example, most people think that setting the water heater thermostat to 120 equates to water coming out of the tap at a constant stream of 120-degree water. In reality, that temperature has a wide operational margin. It may initially be heated to temperatures as high as 145 degrees and cool over time in the tank.

When water heaters are intentionally set high to allow for larger volumes of cold water mixing at the point of use, the risk of scalding increases dramatically. Turning on a cold water tap in the kitchen or flushing a toilet in a second bathroom can reduce the cold water flow during a shower and result in serious burns. Anti-scald devices are designed to prevent this from happening, but many homes don’t have them installed. Tempering valves installed at the hot water outlet can safely allow water tanks to operate at higher temperatures, but they also are not required in most communities.

Warm Water is Dangerous

Setting water temperatures at 120 degrees or lower can be dangerous in a different way. Legionella pneumophila, the bacteria that causes Legionnaires disease, is usually found lurking in the air conditioning systems of hospitals, office buildings or cruise ships. New studies, however, have indicated that 20 percent of diagnosed each year may originate from domestic hot water systems.

The ASSE Recommendation

The American Society of Sanitary Engineering recommends that hot water tanks be set from 135 to 140 degrees, to inhibit the growth of Legionella bacteria, with the installation of anti-scald devices and tempering valves to prevent hot water injuries.

Licensed plumbers should always be hired to make changes to your water system. Custom Air, Inc. is now offering plumbing services in the Lakewood Ranch, FL, area and is available to install anti-scald devices at your shower or tub, tempering valves at your hot water outlet, hot water tank replacement, or even tankless hot water systems. Contact us today for more information!

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