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Thread: 3/4" or 1/2" thermostatic valve

  1. #1
    DIY Member stephenson's Avatar
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    Default 3/4" or 1/2" thermostatic valve

    In a previous post I asked about using a transfer valve for three fixtures in shower ...wife finally decided she only wanted two (shower and a separate hand held) so we shifted from using a transfer valve to using separate volume valves, but local plumbing supply house is telling her she doesn't need 3/4" thermo valve and should use 1/2" - given this is second floor master bath on a well with pressure tank, I think we do, and worst case while more expensive by about $100 it doesn't seem like it could hurt. Thermo valve is Kohler 2975 and volume valves are K 2977.

    I was gonna just T off the output side of the thermo valve and run to each fixture head. Should i just go straight up to a T and run left and right off that, or is it OK to run T "sideways" off line to shower then other fixture off that? i am assuming when one is open and you select the other volume valve there will be some momentary rebalancing since is a simple T design? Could I just use the tub outlet on the thermo valve instead?

    Thanks!

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    Moderator & Master Plumber hj's Avatar
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    Some companies say NOT to use the tub outlet for a shower fixture, but do not explain why. As for the valve size, it depends on how much water you need. A recent test found that if you have a high volume valve and low volume heads the temperature may not stay constant.
    Licensed residential and commercial plumber

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    ACO Shower Drain Sales johnfrwhipple's Avatar
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    Quote Originally Posted by hj View Post
    ... A recent test found that if you have a high volume valve and low volume heads the temperature may not stay constant.
    Interesting HJ - where did you read this study?


    jfrwhipple@gmail.com - www-no-curb.com - 604 506 6792

    Always get construction advice double checked by your local city hall. Flood Test Every Shower - Every Time.

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    DIY Member stephenson's Avatar
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    I was planning on "matching" with 3/4 tstat to 3/4 volume control,or 1/2 to 1/2 if that was the recommendation.

    A further point is that I am using CVPC which has smaller internal diameter than copper or PEX, so 3/4" may not provide that much difference.

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    Moderator & Master Plumber hj's Avatar
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    It was in one of last month's trade magazines, but I cannot remember which one, since I get so many, and was in relation to the current practice of installing a large valve with a "lot" of devices, but only using one or two at a time.
    Licensed residential and commercial plumber

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    ACO Shower Drain Sales johnfrwhipple's Avatar
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    Your 3/4" pipe is not going to be the same as 3/4" copper. Closer to 1/2".

    I would swap out and go with two flow valves verses the "Pick 1of 3 Style".

    It's best when Mommy and Daddy can share the shower and stay warm together. My wife always gets the shower fixture when we take a shower together - I'm not complaining any shower time with Mommy is worth any personal sacrifice I have to make!


    jfrwhipple@gmail.com - www-no-curb.com - 604 506 6792

    Always get construction advice double checked by your local city hall. Flood Test Every Shower - Every Time.

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    DIY Member stephenson's Avatar
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    So, checked with Kohler and they confirmed to just match diameters ... wife ordered the 3/4" versions of the thermostatic valve and two volume valves. Think I'll test it before closing walls in :-)

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    ACO Shower Drain Sales johnfrwhipple's Avatar
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    Isolated the new plumbing work and bring the pressure up to 200PSI and see if your work can hold that for a hour. JW


    jfrwhipple@gmail.com - www-no-curb.com - 604 506 6792

    Always get construction advice double checked by your local city hall. Flood Test Every Shower - Every Time.

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    DIY Member stephenson's Avatar
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    Got the 3/4" valves - nice work by Kohler, and looks to be pretty straightforward to install and plumb. A bit confused now, though.

    I will run 3/4" pipe from tvalve to the volume valves via a simple T ... thermo valve near waist high, then 3/4" up towards the shower arm drop ear with a T between the two that runs to the second valve about a foot away with 3/4 leading to the drop ear for a hand held shower. My confusion ... aren't most shower arms 1/2" ... and, aren't most of the hand held shower supply elbows 1/2"? I have always used 1/2 valves and plumbing ... am I missing something REALLY simple?

  10. #10
    Retired Defense Industry Engineer jadnashua's Avatar
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    INdividual shower outlets are regulated to a maximum of 2.5gpm, so there's not much need to make them for bigger than 1/2". But, reducing fittings are readily available. It becomes a max flow issue when you start to want to run more than one at a time - this is where your 3/4" supply can keep them all flowing at their max.
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Member stephenson's Avatar
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    Thanks ...so just use 3/4 in long runs and reduce to 1/2 prior to the drop ear?

  12. #12
    Retired Defense Industry Engineer jadnashua's Avatar
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    That should work...
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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