When adjusting my hot Water Heater Temperature, what temperature should I set it to? Is the answer different if you have: concerns about diseases, a dishwasher, young children or elderly that can be easily burned, electric vs. gas heat, type of plumbing (e.g. PEX or Copper)? Also, is there a preferred technique to check the temperature of the water after adjusting it?
There are two main and opposing risks:
- Too high, and users get scalded
- Too low, and you risk pathogens, particularly Legionella, which causes legionellosis (Legionnaires’ disease)
Minimum Water Heater Temperature
According to the paper Legionella and the prevention of legionellosis, found at the World Health Organization website, temperature affects the survival of Legionella as follows:
- Above 70 °C (158 °F): Legionella dies almost instantly
- At 60 °C (140 °F): 90% die in 2 minutes
- At 50 °C (122 °F): 90% die in 80–124 minutes, depending on strain
- At 48 to 50 °C (118 to 122 °F): Can survive but do not multiply
- 32 to 42 °C (90 to 108 °F): Ideal growth range
Most current-model dishwashers have a minimum requirement of 49 °C (120 °F). Most have heaters and will heat the interior as needed. If yours is older you may want to check specifications. Dishwasher detergent varies, but “works best between 50 and 60 °C” seems to be a fairly common statement. There is also cold-water detergent on the market that works at basically any temperature.
Maximum Water Heater Temperature
Setting too high can scald someone using the water. This is particularly easy because when you first open the tap, the water in the pipes has cooled down some, and so its temperature will raise (possibly dramatically) once the water from the tank reaches the point of use. Young children are at higher risk because their skin is thinner. Some people, especially the elderly, are at higher risk because they may be less sensitive and slower to move away from scalding water.The Consumer Product Safety Commission (CPSC) recommends setting to 49 °C (120 °F).
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