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Thread: Sizing Residential PRV's

  1. #1

    Question Sizing Residential PRV's

    Greetings Plumbing Guru's

    Can some one help me in sizing PRV or PRV's for my house. And a quick check of my new piping concept would be great too...

    I live in a 1965 home with an inlet pressure of 95+ PSI (has seen 105 PSI), and have many leaking copper joints. Due to the leaking and extensive remodeling plans, I will likely be replacing all plumbing with new L copper (Girlfriend forbids all flavors of plastic in supply lines). Currently I have a 1" M copper supply main from the outside water meter, to the inside main shutoff valve.

    Based on the IRC/IPC (in force where I live), I will have 53.5 fixture units, and I will likely install an 1-1/4" valve manifold (with sub manifolds). Manifold systems (with shut offs to individual loads) are being planned due to the following:
    Staged renovation
    Water closets likely to use recaptured rainwater next year (my bright idea)
    Girlfriend wants high quality water filter on kitchen lines (I like this)
    Girlfriend wants a separate high flow medium quality filter on shower lines (I just smile at this)
    Girlfriend and I hate unexpected temperature changes in shower
    No supply line is greater than 20 pipe feet from manifold to fixture, except front hose bibb

    I have heard from many sources that PRV's need to be sized correctly. If its undersized it will restrict flow and have unacceptable pressure drop off during higher flow rates. If its oversized it will provide ample flow but may create noise at low flow rates.

    Typically its just me and her, but about 4-5 times a year we have as many as 8 total people in the house for about a week at a time.

    Should I install one PRV, or two in parallel. If two, what size(s) should they be, should they be equal size/ different size, recommended initial pressure settings, etc.

    Thanks in advance,
    Renovation Slave

    FYI I do plan to install an expansion tank
    Last edited by Renovation Slave; 05-11-2009 at 09:19 AM. Reason: More information

  2. #2
    In the Trades Gary Swart's Avatar
    Join Date
    Sep 2004
    Yakima WA


    I would get a PRV that was the same size as your water supply line. May be a 3/4" or a 1". Many of the new PRV has a bypass valve the precludes the need for an expansion tank, just make sure if your new one has the bypass or not. You will need a pressure gauge to properly adjust the pressure. Kudos to your GF on the plastic pipe issue.


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