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Mixing Valves

Stokehold Member Posts: 43
In a radiant floor application, can I use a high temperature mixing valve (85-175F) or would it be better to use a low temperature valve (70-120F)? Supply temperature is 140° and I am mixing down to 115°.
Would it be a question of accuracy adjusting the higher temp valve so low? Also, the lower temp valve would seem more applicable to DHW where you would never want the chance of scalding. The flow rate, I believe, is also higher on the high temp valves. There must be a reason why there are two types of valves.
Help here, as always, much appreciated!


  • hot_rod
    hot_rod Member Posts: 22,143
    The low temperature mixing valves usually have a different listing and are intended for point of use, final mixing applications, they cannot be set above 120 for safety reasons. True they are usually a lower Cv valve.

    The main issue when using a 3 way thermostatic is flow rate. A typical 3/4 - 1" mixer will have a Cv of 3 or so. So a 3 gpm flow rate with 1 psi drop.

    Here is an example of a 6 gpm flow rate through a 3 Cv valve, notice the pressure drop.

    So determine what you need for flow rate and see if a 3 way is a good choice.

    In a perfect hydronic world, the Cv number of the valve would match the flow requirement. I would suggest a 5- 6 gpm would be on the high side of what you would want to flow through a 3 Cv valve in a constant circulation hydronic application.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • SWEI
    SWEI Member Posts: 7,356
    Is this a high mass floor? If so, a fixed temperature mixing valve is not likely to produce stable room temps. You want an outdoor reset controlled valve (like a Taco iSeries-R.)