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Do you need to use the mixing valve for Indirect Water Heaters

I posted this as a response to another discussion but thought it might merit a new discussion.

My question relates to Mixing Valves. I just had a 60 Gal Superstore Ultra installed with the optional mixing valve. The documentation mentioned it as optional. I don't believe that either Gas or Electric fired water heaters need them. My question is optimizing efficiency. We got the bigger tank because with the in-line furnace heater we used to have, you could never fill a tub with hot water. Although only two of us now live in the house it is a 4-5 bedroom with 3 full baths and I thought for resale value having a big tank would be desirable for resale. To me it doesn't seem to make sense to heat the tank to 140 degrees, then use the mixing valve to mix in cold to drop down to 115-120 and then again at the tub or sink mix cold again to get to "consumption temperature" of less than 100. This makes sense to me if you need massive amounts of water to supply so that 60 gallons of 140 degree water would probably supply 100 gallons or more of less than 100 degree water. For us, I would think that the most energy efficient settings would be to set the water temperature for the tank to 120 degrees or so and set the mixing valve to maximum (no cold water). This would supply 60 gallons of 120 degree water which when diluted with cold at the sink or tub would be more than we would ever need. Lowering it even more might make sense. We never wash clothes with hot water and the dishwasher has a heating coil to increase the temperature. Anybody have experiences with this?

Comments

  • kcoppkcopp Member Posts: 2,746
    "Need"... Depends. Will it work w/o one yes. As a measure of scaling protection, Yes.
    If the Boiler malfunctions it will protect you.
    Some codes require you to install a listed mixing valve on any water heater. Gas, electric or a tankless coil in a Boiler.
  • Jamie HallJamie Hall Member Posts: 6,655
    One advantage to using the mixing valve is that you can keep the storage tank at a high enough temperature to prevent bacterial growth in the hot water, such as Legionaire's. That means a temperature of 140 as a minimum.
    Jamie



    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.



    Hoffman Equipped System (all original except boiler), Weil-McClain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • IronmanIronman Member Posts: 3,423
    The IMC requires it to prevent scalding in case the aquastat fails.

    As Jamie has said: keeping the tank at 140*+ kills legionella.
    Bob Boan







    You can choose to do what you want, but you cannot choose the consequences.
  • GordyGordy Member Posts: 7,105
    Another thing to add to @Jamie Hall's post. An added plus of higher storage temps is extended usage . However you must protect the end user from scalding. So mixing valve is required.
  • hot rodhot rod Member Posts: 7,014
    If it is a ASSE 1017 listed valve at the tank, you need to keep the tank at 140- 145F. The mixing valve needs a 25-27° difference between hot inlet, and mixed outlet to operate accurately.

    So 145 at the tank mixed to 120F supplied to the building. It good to have that 120 to the washer and dishwasher so the soaps dissolve and work well, for showering you probably mix down to 100° + or -.

    If you have sections of the hot water piping that are not used often, that is where bacteria can harbor and grow.

    With the tank maintained at 140, that should minimize the potential for bacteria to get a start.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • TomTom Member Posts: 455
    Hot Rod,

    What mixing valve can we use to pass code for needing it but with the most minor temp difference for it still to work?

    Most of my customers hate that the state forces the mixing valve and they have caused quite a few headaches, especially when installed on on demands.
    Tom
    Montpelier Vt
  • JohnNYJohnNY Member Posts: 1,811
    Here in NYC, any time a space heating boiler heats domestic water, a temperature limiting device is required.
    For private consulting services, find John "JohnNY" Cataneo here at :
    "72°F, LLC"
    Or email John at John@72fLLC.com
    Or at Gateway Plumbing & Heating
    John travels regularly to out-of-state clients for consulting work.
  • j aj a Member Posts: 1,626
    Limiting devices are very comforting to installers, no one wants issues with occupants,especially young and old getting scalded....It's hard if not impossible to discuss all the different codes in all the different areas this site covers...So I won't, my best advice is to follow the code....
  • hot rodhot rod Member Posts: 7,014
    Tom said:

    Hot Rod,

    What mixing valve can we use to pass code for needing it but with the most minor temp difference for it still to work?

    Most of my customers hate that the state forces the mixing valve and they have caused quite a few headaches, especially when installed on on demands.

    For point of use it must be a an ASSE 1070, It is required to have a tamperproof cap, 120F max.setting.

    At the tank it could be either a 1017 or 1070. The 1070 does have a tighter temperature regulation, but lower Cv.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • j aj a Member Posts: 1,626
    Hot Rod....wondering if that 120 is a national code...last time I went to a code class they said 120 was the minimum and 130 was the max.
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