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DHW mixing valve and check valve requirements?

marktmarkt Posts: 24Member
One DHW mixing valve installation instructions say a check valves are required, another says "if local code requires check valves", another doesn't say...



Is there something about a DHW mixing valve that triggers need for check valves?



Currently I have no check valves, and no expansion tank, in my entire potable system. Nor do I have a pressure regulator (city pressure is 55psi.) I do have a water tank relief valve.



So if I add a DHW mixing valve (and raise tank temp to 140-150), do I need check valves or anything else?
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Comments

  • ZmanZman Posts: 2,331Member ✭✭✭
    Check

    The only check you have to install now are to protect against hot-cold, cold-hot cross connect. Some mixing valves have them built in.

    The other check valves are an entirely different subject.

    Carl
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    ·
  • hot rodhot rod Posts: 4,068Member ✭✭✭✭
    does it have

    a recirc piping and pump? If so the use and installation of checks becomes important.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
    ·
  • marktmarkt Posts: 24Member
    no recirc

    Here's a pic from Caleffi mixing valve install manual for non-recirc system. Any idea why they show check valves (and expansion tank.)
    png
    png
    Screen Shot 2013-08-08 at 8.33.11 PM.png
    0B
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  • Charlie from wmassCharlie from wmass Posts: 3,244Member ✭✭✭
    They show check vales to

    prevent the hot cold water cross flow that was mentioned above. They also show a pressure reducing valve which is why they have the expansion tank in the diagram. The way they show it is the best way to do it when the incoming pressure is high, I figure above 75 psi. The budget does not always allow ffor the expansion tank, and it is not needed unless the expanding water can not relieve  upstream of the tank. The check valves at the valve are required if the valve is installed in MA. I can not speak for other areas.  
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
    https://heatinghelp.com/find-a-contractor/detail/charles-garrity-plumbing-and-heating
    ·
  • marktmarkt Posts: 24Member
    OK, I get the expansion tank

    but what's the problem with a little hot/cold cross flow? Some other manufacturer's install instructions, Taco for example, show no check valves.
    ·
  • ZmanZman Posts: 2,331Member ✭✭✭
    Check

    Mark,

    Some manufactures put integral check valves in the mixer. No need for another in that case.

    Is long as the owner is OK with a little hot in the cold and cold in the hot, don't worry about it. I have found people have this crazy notion that when you turn the hot handle you get hot water and when you turn the cold handle you get cold. The other thing they like is once you set the temp to the shower it stays at that temp. They just don't like it if gets scalding hot when the washing machine downstairs turns on.

    Seriously, if you don't have check valves, slight pressure differences in your system will cause cross flows that will annoy the owner and then, in turn, you.

    Carl
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    ·
  • hot rodhot rod Posts: 4,068Member ✭✭✭✭
    with or without checks

    is how the Caleffi valves are offered.



    Other manufacturers may include the checks, or show a thermal drop in the piping, in their installation manual. Adding the check, of course adds cost and some pressure drop, but does allow more accurate control as Carl mentioned.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
    ·
  • hot rodhot rod Posts: 4,068Member ✭✭✭✭
    another suggestion

    All thermostatic valve will require maintenance and cleaning from time to time.



    How often depends on how hard your water is and how much you run thru the valve.



    The hotter you run your DHW tank, the more it precipitates minerals from the water and they end up where???



    So install the valve with some isolation valves so it can be removed, disassembled and soaked in vinegar or de-limer from time to time.



    There are a number of different ASSE listings for thermostatic valves. Actually a confusing amount of listings that change often :) The last 4 digits is the year the listing was amended for example ASSE 1070- 2003. AHJs can accept different listings in the code.last changed A valve used for distribution is a ASSE 1017.



    A valve used at then point of use or shower, sink, etc is a ASSE 1070. This valve is limited to 120F operation and has some other different operating criteria.



    Valves may also have multiple listings.



    AND of course the Low Lead IAMPO listing may be required in your state and will be nationwide in 2014.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
    ·
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