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Hot water temps revisited

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  • Hot water temps revisited

    A few months back there was a thread about properly setting hot water temps to prevent scalding. Recommended temp was 115F. The gist of the discussion was that setting above this puts individuals at risk of scalding and the plumber at risk of defending his negligence in a courtroom.

    Now comes the article in the Journal of Light Construction that indicates as many as 10,000 people die annually in the US (the author claims this is a middle of the road estimate, the actual number might be substantially higher) as a direct result of hot-water system based bacteria. Apparently 120F is the perfect temp for the legionella bacteria. He claims that the hot water temp should be set to 140F. Setting the temp below 140F put users at risk of serious illness or death. The article goes on to recommend end point anti-scald valves.

    So, apparently we're stuck between a rock and a hard place. I don't know the answer, don't shoot the messenger.

  • #2
    Here is another thread that supports the 140F setting for the same reasons you describe


    • #3
      I think this topic is important, because I've looked at the links provided. My problem is that I see references to a study that water heaters should run hotter, but I don't see the actual study conclusions. Just references.

      Before we begin to install temporing valves in every home in America, we need to see the actual study. If anyone has a link or reference to this please post it. I'm really interested in this.
      the dog


      • #4
        Lots of info including reference text and OSHA links


        • #5
          Good one Wayne, I'll bookmark that for later reading.
          "It's a table saw, do you know where your fingers are?" Bob D. 2006


          1/20/2017 - The Beginning of a new Error


          • #6
            In new housing in my area they are suppose to do what you say with a tempering valve. But the reason they are suppose to do this is more for old people who have slow reaction times and young children who may do it without knowing better. but i am glad that you figured out how to take a shower without burning yourself.
            A restuarant doesn't run there hw at 200f the dishwasher has a booster on it.


            • #7
              I have been adding thermostatic tempering valves for years. I like the idea, it's safer for the end user as well as a more professional installation.
              It also allows for under sizing of the tanks(to a degree). For years I had to up 50 gal. water heaters to 75 gal. to fill up whirlpool and soaking tubs that were used as novelties for the first year or so. Think of the waste of heating such a big tank for very little need. Now in most cases I can fill the same tubs with a 50 gal. set to 140 and tempering valve allowing 120 out.

              Why would a plumber not want to install one? If you answer this question give a better reason than cost please. Cost as a reason is like automakers saying air bags are too costly so lets not put them in cars.


              • #8
                in commercial installations, i see tempering valves. these have to be maintained and serviced. on a large ymca that i just started to call on, they use steam through a heat exchanger to heat thier pools and domestic water. they have to have tempering valves.

                on residential, i've only seen them installed here (l.a.) on domestic heaters when they are also using the water for hydronic heating coils.

                i don't see a need for running higher than 125-130 degree water in a residential heater. in fact all of the heaters have a warning sticker on them and an energy conservation sticker too. the suggested temperature is 125. what i do find is water that is heated too high, 140+, the heaters don't last long and they lime up much faster.

                as far as i know, there is no outbreak of legioneers disease here or elsewhere

                phoebe it is