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HW TANK should be set at 140° F

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  • HW TANK should be set at 140° F

    Instead of hijacking a few threads that are around about hot water tanks I am starting this one.
    There has been much discussion about accelerated tank erosion with higher temperatures and more recently statements that the tank should be set at 122° F.
    I have read that ...
    "The National Research Council has recommended that the water temperature in electric water heaters be set at 60ºC (140ºF) to prevent the proliferation of Legionella bacteria. Legionella thrives in warm water environments, 49ºC (120ºF) or less, but is killed at 60ºC (140ºF) or above."

    If you want to lower the temperature because you have concerns about scalding, a master thermal mixing valve (also called an anti-scald device) can be installed which will limit the water temperature at the tap to 49ºC (120ºF). These devices are now mandatory for new or replacement tanks.

    I am not in the plumbing business so I would like to hear from you guys what the industry thinks. Also the statement I posted only talks to electric heaters, any reason it would be different for a gas fired tank?

  • #2
    wayne, all residential heaters here in the u.s. have a warning sticker on them to prevent scalding. the temperature it states to be set at is 125. the higher it is set, the faster that 1 can be scalded, mainly the young and elderly.

    not to mention a federal energy consumer sticker.

    as far as the difference between an electric and gas, the electric is already factory set behind an access panel upper and lower to 125. i tend to turn these up to 130.

    a mixing / tempering valve is typically installed in a commercial application, such as a restarant. these are prone to sticking and require testing and calibration for safety.
    phoebe it is


    • #3

      Can you tell us what a rental water heater is and why there is a need for them.

      "Somewhere a Village is Missing Twelve Idiots!" - Casey Anthony

      I never lost a cent on the jobs I didn't get!


      • #4
        Perhaps only a northern phenomenon but most gas/utility companies up here actually rent you a water heater, you can buy one at HD or other plumbing stores. They charge you about $14/ month for a 50 gal power vent Rheem and assume all maintenance and service.
        Since Sept 2004 the Ontario building code has been modified so that it is mandatory to install an anti scald device on all new and replacement water heaters. Mine is the Apollo 34A-103-01C

        Rick, is the valve above the type that you are referring to? What would you recommend as a testing frequency?

        Can I assume that neither of you have heard of "Legionella bacteria" building up in a water heater


        • #5
          Legionella is the bacteria which causes Legionnairs Disease. I'm not sure why but we do not really have a problem with it in our potable water. Perhaps it is the way we treat our water. I am required to test for it but because of my water source and location of my tanks and systems I am not very likely to have any. Typically if we have it here it is from a cooling system.

          "Somewhere a Village is Missing Twelve Idiots!" - Casey Anthony

          I never lost a cent on the jobs I didn't get!


          • #6

            Temperature Time to Cause
            of Water a Bad Burn
            150°F (66°C) 2 seconds
            140°F (60°C) 6 seconds
            125°F (52°C) 2 minutes
            120°F (49°C) 10 minutes
            One of the best lessons I learned from my father is when he did nothing to help me. I then learned to help my self.


            • #7
              I run a personal care home and by law the water can NOT be over 120 f.

              Am I at risk for conatamated water??


              • #8
                At Risk?...maybe.

                I have heard that the requirement may be changed to increase the water heater temp to 140F and install anti-scald or tempering devices that conform to ASSE Std 1070 and are be set to deliver 120F water and to sinks, showers, etc. Dishwashers and clothes washers would get the full 140F water, i.e. not tempered. This kills the Legionella but guards against scalding. I think there is something in the proposed change that the tempering valve must be located within 3 feet of the point of use.

                You can get an idea of what COULD be coming up in the way of changes by reviewing this list of proposed changes to the 2006 UPC.

                Look at Item #83 on pg 25 for one proposal, item # 93 on pg 40 is another.
                Last edited by Bob D.; 05-22-2006, 08:13 PM.
                "It's a table saw, do you know where your fingers are?" Bob D. 2006



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


                • #9
                  wayne, that's pretty much the valve we too use. interesting fact about the renting of a water heater. at $14 a month x 12 months = $168 a year x 10 years = $1680. not a bad gimmick. does this include installation cost and replacement?

                  bob, you amaze me with all the facts and research data that you post.
                  keep them coming. i need to refresh my brain cells

                  phoebe it is


                  • #10
                    Rick, you would have to pay for the initial install (gas pipe or electric wire, water connections, mixing valve, and vent) but if for any reason the tank needs to be replaced the utility company covers all costs to swap tanks and disposal of the old tank.
                    The mixing valve is considered part of the house system so there has been some uproar from the renters when they find out they have to pay for it to be installed.
                    Every house I have lived in has had a rental water heater including my moms first house back in 1979. The utility companies are in with the builders