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What is the "safe" minimum temperature a water heater should be set?

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What is the "SAFE" minimum temperature a water heater should be set?

Safe Hot Water - Serving Winnipeg and area since 1970, Custom Vac provides a full range of heating and air conditioning services, water tank sales, and 24 hour emergency service. There are really two issues when we discuss potable water systems, they are; temperature setting of the water heater (source) and distribution system; and the temperature setting of the water at the point of use. Lets separate them to avoid confusion and allow us fully explain the differences and hazards. Most homes only have one temperature, that of the water heater. Maybe after reading more on this topic you'll be convinced to go beyond how most water heaters are installed.

Point-of-use (Fixtures)

Lets deal with the point-of-use first. Dr. D Brynum presented a technical paper in 1998 for the ASPE titled Domestic Hot Water Scald Burn Lawsuits "The Who, What, When Why, Where, How" some of the information here been take from that paper.

What do we know? 120ºF water temperature at the point of use is not safe. The pain threshold for most people is 106ºF. Lowering of water heater temperatures to 120ºF is not safe either, and in fact, most people who lower setting to 120ºF, raise the temperature setting again, because they find themselves running out of hot water at this setting.

At 120ºF 3rd degree burns occur within 3.1 minutes for children and 4.8 minutes for adults. Compare this to water temperature at 140ºF where it takes only 0.7 seconds for a child and 2.8 seconds for an adult. Worse yet is 150ºF where it takes 0.5 seconds for a child and 1.8 seconds for an adult.

Another especially hazardous condition is known as the "stacking effect," this is more pronounced in gas water heaters due to the aggressive manner in which they heat water. This stacking occurs due to the natural rise of hot water in the tank, kind of like stacking pancakes, each at a different temperature, cooler ones below and the hot ones stacked on top. As an example, a water heater set to maintain 130ºF without a circulation pump could have water temperatures between 130ºF at the bottom and 190ºF at the top, a very hazardous condition.

We know according to data from the National Safe Kids Campaign that between 4,000-5000 children are scaled each year, most often in bathtubs. The average bathtub scald covers 12% of the body surface with a full thickness third degree burn. Statistics also indicate that the scald burn sources were 95% residential settings (54% in apartment houses and 46% in single family homes.)

Did you know?

Severely burned Children require constant skin grafts as they grow.

Grafted skin does not regenerate and must be replaced often until growth of the person stops.

Scalding is a serious safety hazard to children and the elderly, and yet research scientists, manufacturer's and code committees cannot agree on what that safe temperature should be. You do not need to wait until a code is established to act to protect your children now. Take the knowledge you've learned and implement the changes now before one of your family members are injured. Consider point of use temperatures well below 120ºF.

Point-of-source (Water Heater)

Water heater temperatures should be maintained at 135ºF or higher up to the point of use to keep Legionella bacteria out of the potable water. Water heaters set at 120ºF may save some energy, but they DO NOT protect people. In order to contract Legionella bacteria, one needs to be exposed to atomized water, such as in a shower, which is the perfect environment.

FACT: Random blood sampling by the Center for Disease Control (CDC) in the US revealed that 95% of Americans have been exposed to the Legionella bacteria.

Contributing factors to the growth of Legionella Pneumophila bacteria are.

  • Temperatures between 55ºF - 133ºF

  • PH levels between 5.0 - 8.5

  • Bio film

  • Stagnation

These conditions can be found in almost every home. Water heater temperatures of 55ºF - 133ºF are all too common. PH levels are very close to 5.0 - 8.5. Bio-films are found on the walls of all piping and in water heaters and stagnation is equally as common since not all point of use fixtures get use and many times, dead end piping is found where water will sit forever, which is why is so important if old water lines are going to be capped off, that they be capped off at the distribution main, not at the most convenient place.

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