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Thread: Can pex be used with Moen tub/shower with handheld shower -commercial 8343

  1. #1
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    Default Can pex be used with Moen tub/shower with handheld shower -commercial 8343

    Hi,

    We are renovating our bathroom and are going to go with installing the Moen 8343 Double Handle Posi-Temp Tub and Shower Valve with Handshower from the Commercial Collection. http://www.moen.com/commercial/chrom...MERCIAL%3A8343.

    My question is can pex be used on any sections of this install? The instructions show doing the whole thing in copper.


    There will be so many 90's and 45's needed to make all the pipe get to where they need to be and bypass one another that is seems pex would be so much easier and eliminate a ton of fittings. But the instructions say nothing about using pex or no using pex.

    Thanks for any help you can give,

    Kim

  2. #2
    Test, Don't Guess! cacher_chick's Avatar
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    Because PEX has a smaller inside diameter than copper, it is not recommended. In some cases, it can cause water to still come out of the shower head when the tub is being filled.

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    This has a separate Temp valve before the diverter valve. Could we bring to pex right up to the temp valve and then switch to copper? Or do we need to stop the pex before we even get close to the hot/cold mix valve?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    You likely will want all the volume possible from the new installation...if the valve expects 1/2" pipe inlets, use 3/4" pex to it and it should be fine. Using 1/2" pex would likely offer too much of a restriction, and thus limit your volume which may exhibit itself as reduced pressure. If the valve is 3/4" inlets, use 1" pex to maintain the same volume capability. Now, if this is only using a hand shower, and you don't plan to also fill the tub, it probably doesn't matter as long as it's only one head - this assumes it's one of the typical, gpm restricted heads used residentially. It really depends on how much volume (gpm) you expect out of the valve and what you need at the outlet. Less than 4-5, pex at 1/2" would work. More, you'd need 3/4" or more, again depending on the volume you need or want.
    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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    Moderator & Master Plumber hj's Avatar
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    1/2"' PEX to the valve and to the shower head is the common way to do it, when using PEX, but NOT to the tub spout. That has to be copper, brass, or steel to allow full flow.
    Licensed residential and commercial plumber

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    Ok,

    So just to be clear. Both the temp valve and the diverter valve are 1/2". Should we use 3/4" pex to maintain the volume or use 1/2" PEX. In looking at the 1/2" PEX fitting compared to 1/2 copper fitting I can see that the pex is a smaller opening.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Will you be trying to fill a tub in addition to the shower head? How many gpm is the shower head? If you want to fill the tub as fast as possible, use the 3/4", if it's only a shower head...you still didn't indicate how many gpm it is rated at. Commercial stuff may differ from residential, but 1/2" pex would be fine for a single shower head if it's the normal, 2.5gpm type. A medical/commercial unit might be more, lots more - then more volume would be a big factor.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  8. #8
    Moderator & Master Plumber hj's Avatar
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    The specifications say "1/2 inch connections AND 2.5 gpm MAX" which would indicate that 1/2" PEX to the valve would be more than adequate.
    Licensed residential and commercial plumber

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