Pipe size with added shower sprays etc.

Discussion in 'Shower & Bathtub Forum & Blog' started by 2020Bob, May 20, 2020.

  1. 2020Bob

    2020Bob New Member

    Dec 23, 2019
    Building new home the builder typically uses 1/2" cpvc for single shower (no tub)

    he wanted a small fortune to upgrade to the addition of rain fall & 3 massage sprays.

    I think 1/2" is rated at about 14gpm, granted not all will be on at the same time, is 1/2" adequate?

    I asked him to just build with standard shower I will upgrade after closing, have good access from joining room to get to plumbing without redoing tile.
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    IMHO, 1/2" line to feed 14gpm won't work well.

    Keep in mind that most all 1/2" valves are only rated for 5-6 gpm. To achieve 14 gpm, you'd need at least a 3/4" valve and supply. Note, those numbers are when using copper which has a larger ID than CPVC. A code compliant showerhead cannot draw more than 2.5 gpm, and sprays can also be anywhere up to that amount as well, so let's say you want one of the showerheads and the side sprays on at the same time, that could be up to 10 gpm. Not going to happen with a 1/2" valve. If the sprays are more in the order of 1 gpm, you have a chance, but it still would be shaky because of the smaller ID of CPVC versus copper. CPVC doesn't have the same issue with max flow velocity that is recommended for copper, but the faster you flow through the pipe, the greater the dynamic pressure loss you'll have. The static pressure should be the same everywhere (well, except for elevation differences), but the dynamic pressure loss starts to go way up as the velocity goes up, and it can result in water flow noises in the pipes, too.
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