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Thread: Is 1/2" PEX supply big enough for dual shower head?

  1. #1

    Default Is 1/2" PEX supply big enough for dual shower head?

    I am planning to pick up one of those Moen 3 way diverter units but my biggest concern is having the pressure drop off in the dual headed shower when my wife turns on the second shower head.

    I have read on this forum how PEX internal diameter is smaller than copper but I called Moen and they confirmed that a 1/2" line was all I needed to supply the 3 way valve.

    Does anyone have here a bad experience to share with the 3 way diverter units? I would hate to get the thing plumbed in a only to find that it doesn't work well..... Thanks.

  2. #2
    Moderator & Master Plumber hj's Avatar
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    Default Pex

    Asking Moen that question is probably the same as asking the ********* aisle person. They do not install them so how would they know?

  3. #3

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    I figured that at least the manufacturer would be able to tell me because they had done tests or something during development. I have to think that somebody out there knows what they are talking about. If it ain't the manufacturer, who might it be?

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    Plumber Cass's Avatar
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    Much of the answer your looking for will depend on your dynamic water pressure and flow coming to the house and ultimately your shower.

    I have 1 customer who's house has a 1/2" line coming from the street and his water pressure is 38# static. There is no way he could run 2 showers at the same time satisfactorily.
    Last edited by Cass; 06-05-2007 at 02:22 AM.

  5. #5
    Moderator & Master Plumber hj's Avatar
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    Default Moen

    Yes, they run tests, but do you really thing they use the smallest pipe in their laboratory? They could have a 1" supply line for their tests, but the guy on the phone has no clue as to what they use when they connect the piping for flow tests. All they are worried about is how much water will flow through the valve, so they make sure enough water is getting to it.

  6. #6
    DIY Senior Member ToolsRMe's Avatar
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    I like a GREAT shower. The federal regulations on a shower head are a distraction for me so I remove the flow restrictor. I'm a bad boy but I figure it is not the government's business whether I take a shower or a bath.

    About a year ago I did a remodel of the house I just bought. I made sure that I ran 3/4 copper to the valve.

    Then I made a mistake and bought the 1/2" Hans Grohe 3-way valve. I did it because my wife liked the looks.

    If I had to do it all again, I'd definitely cough up the extra money to go with a 3/4" valve. Don't get me wrong, the 1/2 3-way valve is GOOD but it is not GREAT.

    In my case the company's web site had the flow rates for the valve. If I remember correctly mine was 14 gpm. The 3/4 was 18. (I'm not sure of these numbers!)

    So I looked up some numbers on one pair of Hansgrohe mixing valves for you

    1/2" 15373181 13.2 GPM @ 44 PSI
    3/4" 15374181 20 GPM @ 44 PSI

    Tracking this information is a bit difficult. I wish I could remember where the flow rate v. pressure charts were when I saw them a year ago.

    Anyway, good luck.
    Last edited by ToolsRMe; 06-05-2007 at 11:44 PM.

  7. #7
    Plumber Cass's Avatar
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    Quote Originally Posted by ToolsRMe
    1/2" 15373181 13.2 GPM @ 44 PSI
    3/4" 15374181 20 GPM @ 44 PSI
    I will guess that the 44 PSI is a dynamic pressure and not static as static would be meaningless.

  8. #8
    DIY Junior Member insulated's Avatar
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    KS HANDI
    I am doing the same thing, except I plan on running a rain head hand held, and 3 body sprays. Total output 9gpm. I have a 3/4" thermo valve and 3 volume valves, one for each. Danze publishes flow rates through 1/2" and 3/4" copper at various pressure. At 45 lbs it tells me I am delivering about 12gpm with 1/2". Seems to be more than enough even with pex. I'm going to do something before the weekend. Let me know your thoughts.
    ( I doubt all 3 heads will be on at the same time)
    I also have called 4 master plumbers to the job site,( totally mixed answers) 3 manufactures,(all say it will work, even with pex.) And have been on the web for hours. I have found a plumber that specializes in shower systems. He said he does it every week without a problem. He is coming today.

    I do know most homes here in Texas only have 1/2" in the bathrooms, so starting with 3/4" isn't reasonable. Most manufactures wouldn't want to give up the Texas market. They would have found a solution to bigger showers so they could sell more product without 3k worth of re piping. I am just amazed that no one has personal experience with such a large part of the remodel industry wanting custom showers. I don't think tearing up the walls ans slab is the correct solution.

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