Supply needed for 2 shower valves

Discussion in 'Shower & Bathtub Forum & Blog' started by kingcledus, Feb 8, 2006.

  1. kingcledus

    kingcledus New Member

    Feb 7, 2006
    I'm in the middle of remodeling my master bath. We are installing a 5' walk-in shower and I had my heart set on installing two posi-temp Moen valves and two shower heads. I found the water supply to the bathroom is only 1/2" copper.

    Will this have the capacity to use both shower valves at the same time? I don't mind a slight loss of pressure when using both so long as they function properly.
  2. Cass

    Cass Plumber

    Nov 12, 2005
    Your performance will not be what your looking for/expecting if all you have is 1/2 " feeding them, if they are used at the same time. Can you change the line from the water heater to 3/4"? If you can feed each valve seperately off the 3/4" line. Is the line feeding the water heater 3/4" also?
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  4. plumber1

    plumber1 Plumber

    Aug 7, 2005
    I agree with Cass. I think he is saying that you need "volume". But if you have high pressure, that will get you more water to each.

    But if you re-pipe, it's the best thing to do......
  5. kingcledus

    kingcledus New Member

    Feb 7, 2006
    Thanks for your thoughts. That is what I was afraid of. It is a second story bathroom, and the water heater is in the basement, so repiping will be more of a challenge than I care to take on for this house.
  6. Bob NH

    Bob NH In the Trades

    Oct 20, 2005
    New Hampshire
    They should function properly and it is possible that you would get satisfactory performance.

    Shower valves are supposed to be limited to 2.5 GPM so two of them will be using 5 GPM, unless you get rid of the flow limiter.

    Pressure drop for 1/2" type M copper is 0.13 psi/ft at 5 GPM, so in 40 ft and adding a bit for losses at elbows, you might lose 7 psi.

    If you keep your water heater set at a higher temperature, such as 140 F, you will be mixing some cold with the hot so the flow through the hot water line will be reduced.

    You don't say what your water pressure is. If you are on a municipal system it might be high enough that the loss in the pipe won't matter.
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    Did you look at the Grohe Freehander? It would simplify installation (one valve, unless you want to both be in there with your own at the same time).
  8. jimbo

    jimbo Plumber

    Aug 31, 2004
    San Diego, CA
    I would check the post 3 down from this one about : "hot water puzzle". I suggested that 2 pressure balanced valves plumbed together might be fighting each other. That poster has requested feedback from Price Pfister on the issue. Results should be informative.
    Last edited: Feb 8, 2006
  9. kingcledus

    kingcledus New Member

    Feb 7, 2006
    Thanks for all the help. This site is great.

    I have not had my water pressure checked, but I would rate is as good. The risk of it not working correctly using one supply has made me decided against the two valves on one supply. There is a second half inch supply on the other side of the bathroom from the small shower I ripped out that I am going to use for another vanity. It looks to me near impossilble to branch it across the room to use for a second shower valve, but I am going to get a plummer to look at it.
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