Which PEX sizes according to ...

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by diy-mark, Jul 6, 2008.

  1. diy-mark

    diy-mark New Member

    Messages:
    25
    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/DesignGuides/pex_designguide.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. diy-mark

    diy-mark New Member

    Messages:
    25
    I see that the Lowe's in my area is selling Zurn PEX.

    Is this a good brand?
  3. 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....
    Last edited: Jul 6, 2008
  4. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,631
    Location:
    Cave Creek, Arizona
    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. diy-mark

    diy-mark New Member

    Messages:
    25
    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. diy-mark

    diy-mark New Member

    Messages:
    25
    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. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    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. Redwood

    Redwood Master Plumber

    Messages:
    7,450
    Location:
    Connecticut
  9. diy-mark

    diy-mark New Member

    Messages:
    25
    manablock syster?

    Could somebody please explain what the poster meant by that comment.
  10. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,631
    Location:
    Cave Creek, Arizona
    ?

    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. diy-mark

    diy-mark New Member

    Messages:
    25
    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. diy-mark

    diy-mark New Member

    Messages:
    25
    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. manibloc system

    Last edited: Jul 6, 2008
  14. diy-mark

    diy-mark New Member

    Messages:
    25
    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. Bob NH

    Bob NH In the Trades

    Messages:
    3,317
    Location:
    New Hampshire
    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: Jul 6, 2008
  16. jastori

    jastori New Member

    Messages:
    118
    Location:
    Illinois
    Tubing size for tub/shower vs. shower only

    Regarding the discussion about why a tub/shower would need larger piping as opposed to shower only (this is only a non-professional guess)...

    If we assume that a low-flow showerhead is used, then the shower would be limited to 2.5GPM (or is it 2.2?).

    However, you may want a higher flow-rate when filling a tub. I thought that a tub filler might be something like 4GPM?

    If so, it seems reasonable that you might not want 3/8 tubing for a tub filler, but it might be OK for a low-flow showerhead.

    Sorry if this is off-base.... just a thought.
  17. diy-mark

    diy-mark New Member

    Messages:
    25
    It's true I can use CPVC but I can't follow the same route that was used by the copper because in some areas, I can't get to the copper. For instance, in some places it's buried under the stem wall and I'm not going to dig for it.

    And I'm thinking the more joints, the more potential problems and I've seen some plumbers on this forum saying that CPVC is 'junk'.

    But anyway, your advice is good and your points are something I'll have to definitely take into consideration.

    And yes, I will certainly save whatever old copper I'm able to salvage out of here regardless of what I put back in.

    Thanks for your input. :)
  18. diy-mark

    diy-mark New Member

    Messages:
    25
    Since I don't even have a tub in this house, the 3/8 is sounding better and better.

    Also, we've got a septic tank here so the amount of water going into that is also a consideration. Bigger pipes = more waste.

    On the other hand, based on what has been said here, there are definite advantages to going the 1/2 inch CPVC route. Home Depot is the closest place to me (about 1 mile) and they don't sell PEX.
  19. Bob NH

    Bob NH In the Trades

    Messages:
    3,317
    Location:
    New Hampshire
    CPVC has a long and successful history in industrial uses. You don't have freezing problems which is sometimes given as a reason to use PEX.

    If you are working in a crawl space you can run 1/2" CPVC through joists or under the joists. You will need a lot of hanger clamps.

    The cost of PEX fittings leads to a lot of use of Home Runs. With CPVC it is more common to use standard tee-and-branch routing but you could use home-runs if you thought it was easier or better.

    I think you will find that all of the fittings in CPVC will be less than PEX, especially when you consider the valves, manifolds you don't need, and the tools you won't need.
  20. diy-mark

    diy-mark New Member

    Messages:
    25
    How would you use home-runs? Do they sell some kind of manifold for that?
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