The REAL Ideal Temperture Setting For Your Water Heater

Author: Pacific Northwest Inspections Group, LLC   Date: 13-Apr-2017.   Category: Plumbing   Add to Favorites 

We all hear that 120 is the recommended setting from local and State departments, but is it? 

What happens at 120 degrees?

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)
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    At 120 degrees bacteria can survive but does not multiply. It takes 8min for a 1st degree burn. Dust mites are not killed at this 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

    It also takes 131 degrees to kill Dust Mites.

    Ideal Water Temperature