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Thread: Which PEX sizes according to ...

  1. #1

    Default Which PEX sizes according to ...

    In my small house I'm considering changing my whole system to PEX. Manifold system. A 3/4 inch pipe will run to the manifolds.

    According to a PEX design guide pdf file I downloaded the other day

    http://www.toolbase.org/PDF/DesignGu...esignguide.pdf

    3/8 inch pipes can be run from the manifolds to most fixtures. Can anybody verify that this will work out ok?

    This is what it says according to the above guide, in section 1:75.

    Minimum Sizes of Fixture Water Supply Lines
    in Manifold Systems


    Fixture - Minimum Pipe Size(in.)

    Bathtubs and Whirlpool Tubs - 1/2
    Tub and Shower - 1/2
    Shower only (Single Head) - 3/8
    Bathroom Lavatory - 3/8
    Water Closet, Residential - 3/8
    Water Closet, Commercial - 1/2
    Kitchen Sink - 3/8
    Laundry Washing Machine - 3/8
    Utility Sink - 3/8
    Bar Sink - 3/8
    Urinal, Flush Tank - 3/8
    Urinal, Flush Valve - 1/2

  2. #2

    Default

    I see that the Lowe's in my area is selling Zurn PEX.

    Is this a good brand?

  3. #3
    Master Plumber master plumber mark's Avatar
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    Talking not good , but it will work

    I have seen one fellow do this in his home,

    I was not very impressed with it..although it will
    probably work ok becasue all faucest and stops will
    eventually funnel down to that size at the fixture...

    the pressure balanced faucets would concern me and I
    would rather opt to run 1/2 pex everywhere instead..
    its realy not that much trouble or expence to run the 1/2 over
    the 3/8 anyway ...


    But You could also mix them up with 1/2 going to all the
    larger bath faucets and 3/8 going to the toilets and lav faucets.


    Zurn Pex has a class action lawsuit on their brass fittings right now.
    I would not trust it........

    stick with the stuff that the manablock system wants you to use....

  4. #4
    Moderator & Master Plumber hj's Avatar
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    Default sizes

    At least two questions with that table.
    1. Why would a shower only need smaller pipes than a tub/shower. You either use the tub or the shower only so it should use the same amount of water as a shower only.
    2. What is the difference between a residential and commercial water closet? The water supply just fills the tank on either of them and the water in the tank flushes the toilet, and has nothing to do with the incoming water supply.

  5. #5

    Default

    Quote Originally Posted by master plumber mark View Post
    I have seen one fellow do this in his home,

    Zurn Pex has a class action lawsuit on their brass fittings right now.
    I would not trust it........

    stick with the stuff that the manablock system wants you to use....
    It looks like Lowes only sells 1/2 and 3/4 inch anyway, so that takes care of the size issue.

    I don't understand what you mean in your 'manablock' comment. It looks to me like Lowes only sells Zurn PEX.

    Do you know what the problem was with the brass fittings?

  6. #6

    Default

    Hi hj,

    I can't really answer your 2 questions.

    1. Maybe they figure some people will be filling the tub while they take a shower?

    2. Maybe they figure a commercial toilet needs to fill faster to accommodate the next 'customer'?

  7. #7
    Plumber jimbo's Avatar
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    Default

    The brass fittings were poorly designed and manufactured, and they BROKE.

    A commercial toilet might imply a flushometer, which has a need for greater water flow, even though total flush still is 1.6 gpm

  8. #8
    Master Plumber Redwood's Avatar
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  9. #9

    Default manablock syster?

    stick with the stuff that the manablock system wants you to use....
    Could somebody please explain what the poster meant by that comment.

  10. #10
    Moderator & Master Plumber hj's Avatar
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    Default ?

    1. Maybe they figure some people will be filling the tub while they take a shower?

    Can't be done with most tub/shower valves.

    2. Maybe they figure a commercial toilet needs to fill faster to accommodate the next 'customer'?

    They only fill as fast as the toilet's valve passes water, and that valve is the same for both types of toilet.

    A flushometer commercial toilet needs a minimum 1" line and probably 1 1/4" PEX, so that throws that theory out the window also.

    My questions were asked to throw suspicion on the experience and knowledge of whoever composed the table.

  11. #11

    Default Who prepared the pdf file?

    If I'm not mistaken, I provided a link to the file further up the thread.

    Here's what it says on the second page of the file. (the logos probably won't post)

    Prepared for
    Plastics Pipe Institute, Inc (PPI)
    105 Decker Court
    Suite 825
    Irving, TX 75062
    www.plasticpipe.org

    and

    Plastic Pipe and Fittings Association (PPFA)
    800 Roosevelt Road, Bldg. C, Ste. 312
    Glen Ellyn, IL 60137
    www.ppfahome.org

    and

    Partnership for Advancing Technology in Housing
    451 7th Street, SW
    Washington, DC 20410
    www.pathnet.org

    Prepared by
    NAHB Research Center, Inc.
    400 Prince George’s Boulevard
    Upper Marlboro, MD 20774
    www.nahbrc.org
    November 2006

    This document was developed as the result of a consensus process involving the Plastic Pipe Institute, the Plastic and Plastic Pipe and Fitting Association, and representatives from numerous piping and fitting manufacturers. It was prepared by the NAHB Research Center, with support and research from the Partnership for Advancing Technology in Housing (PATH).

  12. #12

    Default No Pro

    I'm not a professional plumber. And I really could care less why some document says 3/8 inch as opposed to 1/2 inch for commercial as opposed to residential. Those are technicalities I don't give a load of crap about.

    All I am is a little diy guy trying to put together a half-way decent plumbing system in my 60 year old 500 square foot wooden cottage in South Florida, that my wife and I live in ALL YEAR LONG. And we have lived here since 1973, when I got out of the Navy.

    When my grandparents died, I basically 'inherited' this place. They paid $6000 for the place back in the 60s. And now the copper feed pipe is breaking down and I want to replace the whole system.

    Actually, plumbing is my LEAST favorite type of job but I'm going to tackle this job anyway because I WANT to and because I've done every other thing around here, including electrical, carpentry, concrete work etc. My wife and I built a work shop and two other out buildings on this property. BY OURSELVES. Permits and inspections included.

    This particular job may or may not be 'permitted', because as far as I'm concerned it's a 'repair', which in reality is exactly what it is and I'm an American who believes we still have a few freedoms left in this country and we better take advantage of them while they last, which probably won't be much longer if the frikkin' liberals have their way.

    The bottom line here is that I joined this forum to get sound advice, not to argue technicalities with professional plumbers.

  13. #13
    Master Plumber master plumber mark's Avatar
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    Talking manibloc system

    [quote=diy-mark;144858]In my small house I'm considering changing my whole system to PEX. Manifold system. A 3/4 inch pipe will run to the manifolds.



    so sorry to confuse you, the manibloc system is
    what I thought you were going to use with the 3/8th pipeing

    I will find a picture of one and post it...

    Just Google Manibloc plumbing systems and you will run
    into plenty of pretty pictures like the ones below and lots of information


    this is probably what I would use if I were a total novice at plumbing
    and of course you can run the 3/8th is you so chooose to

    it seems to be very popular around here and you can string the lines
    all the way through the house to each fixture
    from the main manifold or manibloc...........




    http://www.pexsupply.com/pex-manabloc.asp

  14. #14

    Default Thanks Mark

    Now we're talking turkey.

    If I can't get it locally, I don't mind having it shipped in because I'm not in a big hurry here.

    The only drawback is if I forget to order something and can't go out and get it in the middle of the job.

  15. #15
    In the Trades Bob NH's Avatar
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    Default

    With the project as you have described, I would not mess with the PEX. I would use CPVC. It is simpler to use and will cost less.

    http://forum.do ityourself.com/showthread.php?t=103305 (paste into browser and delete the space)

    You can run 1/2" CPVC to everything, following the route that was used by the copper. You can run 3/4" "main lines" if you want but I prefer 1/2" for all hot water lines because it wastes less water getting to the fixtures.

    The reason that larger pipes are often specified for tubs is that you want larger flow for a quick fill of the tub; while showers are limited to 2.5 GPM per head.

    You can get all of the material at HD or other big-box stores. Be sure to use cement that is designated for CPVC.

    The 1/2" CPVC is slightly smaller inside diameter than 1/2" copper but the runs are going to be pretty short in a 500 sq ft cottage.

    Some places they tell you to run something other than CPVC for the first foot or so from the hot water heater. That is not a big deal if you have to do it.

    The PEX will cost a lot more for fittings and you have to buy special tools.

    The CPVC can be run through stud walls because it is quite flexible.

    Save the copper to be sold for scrap. It is quite valuable.
    Last edited by Bob NH; 07-06-2008 at 03:36 PM. Reason: Add link

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