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Thread: Multi-outlet shower plumbing

  1. #1
    DIY Junior Member oreke's Avatar
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    Default Multi-outlet shower plumbing

    Hi All,

    I am planning to build a multiple outlet shower, with potentially a rain shower head (2.5gpm), regular shower head (2.5gpm) and four body spars (1.75gpm each). I am calculating a max of 12gpm if I were to turn all of them on at the same time, which should be a rare occasion.

    I have 3/4" lines through most of the house. A 1/2" line tees off from the 3/4" and goes for about 10ft to this shower. I have regulated the pressure to 65psi.

    My plan was to get a pressure balanced shower valve and three volume control valves for each outlet. As far as I have seen, 1/2" input shower valves have flow rates of 6-7gpm. Whereas 3/4" input shower valves have 10-16gpm flow rates (Have checked Moen and Kohler). My questions are:

    1) Are there higher flow rate, 1/2" shower valves that anyone would recommend?
    2) If I were to get a 3/4" shower valve and go up to 3/4" piping from the 1/2" I have, would the shower work properly? I would end up with 3/4" lines, then a 1/2" run for about 10ft, then 3/4" for about 3ft before the valve.

    Thanks,
    Oreke

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    A very short section of 1/2" pipe would not restrict the flow too much compared to all 3/4", but a 10' section means you have essentially a 1/2" line if I understand it properly. Higher flow rates in a 1/2" pipe can cause erosion and noise issues, so getting more out of a 1/2" valve is not likely. One way to maximize it is to make the hot hotter...this means that you'll use more cold to get it the proper temperature for your shower. On a more common situation, with the WH set to a typical (safe) 120-degree max, you are using mostly hot in the winter, and only a little cold to temper it down to where you want it. But, if the hot is hotter, you'd use more cold. The flow from both the hot and the cold together would be higher. The internal passages aren't all that large, so it may not end up making all that much difference. Much better to go with 3/4" for what you are trying to do.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    One who lurks Basement_Lurker's Avatar
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    I can see that you have put a lot of thought into this setup, and I can appreciate that, but I can tell that this is above your skill level. A multi-function shower system like this is not a DIY project, and you definitely need this planned out properly. I suggest you consider hiring a professional to do this installation, and that you put your time into interviewing EXPERIENCED installers to ensure this is done properly. However, FYI, a 3/4" valve is definitely the best way to go, but using 3/4" pex to make your conversions would be a total waste of time and money....
    Broken promises don't upset me. I just think, why did they believe me? -Jack Handy


    www.blackbirdkitchenandbath.com

  4. #4
    Moderator & Master Plumber hj's Avatar
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    IF you look at the actual openings in a 3/4" valve, you will see they are actually two "pie shaped wedges" and if you calculate their areas, you will find that the total is probably SMALLER than the area of a 1/2"' copper tube. Therefore, using 3/4" tubing will SELDOM produce significantly higher volumes of water, and almost definitely not anything you will be able to notice.

  5. #5
    DIY Junior Member oreke's Avatar
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    Default

    Thanks for the replies. I recently looked at a table of flow rates for copper pipes, which I don't currently have with me. I remember that the max flow rate for a 1/2" pipe at 60psi was larger than 12gpm, even for lengths longer than 10'. This seems to make sense given the information hj has provided. The valve flow rate is limited by the actual openings at the inputs as opposed to the size of the pipe going into them.

    Correct me if I am wrong, but I understand the general suggestion to be a 3/4" valve that has the higher flow rate. The 10' 1/2" section should easily be able to provide 12gpm. I just need to go from 1/2" to 3/4" pipe in order to be able to connect to the 3/4" valve.

    Are there any other issues that I should be concerned about?

    Just to recap my main issue:
    - I need 12gpm
    - I have 1/2" piping for about 10ft. teeing off from a 3/4" line
    - 1/2" input shower valves go up to 7gpm, so I should use a 3/4" shower valve that can supply 12gpm
    - If I use a 3/4" valve, will the 1/2" line be a limitation? (The answer to this seems to be "No")
    - If I go from 1/2" to 3/4" for about 3ft, should I be concerned about any issues?

    Much obliged,
    Oreke.

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
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    How much a pipe CAN flow, and how much it SHOULD flow are two different things! If you can get to that section later, try it, then if it doesn't work, change it to 3/4".
    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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