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Thread: 1/2 copper to 1/2 or 3/4 pex?

  1. #1
    DIY Member lemmy's Avatar
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    Default 1/2 copper to 1/2 or 3/4 pex?

    I am renovating a bathroom and I am moving the toilet and shower/tub so the water lines needed to be re-routed. I cut back the 1/2 copper supply lines then I will use a sharkbite push on connector to convert to PEX, then I will run the pex to the new locations. I have purchased 1/2 pex but after doing some reading at some other places that I trust less then those on this forum, I have seen people suggest that it is better to go from 1/2 copper to 3/4 PEX. The PEX run will only be about 10'-12' so I am not worried about having to wait a little longer for hot water to arrive.

    Also, when possible should I always try to minimize using elbows? I was trying to make a 90 with the 1/2 PEX and was using one of those metal 90 degree supports and the PEX seemed to crimp/collapse some in the middle when I snapped it in. I know these are supposed to be set to the correct bend radius, but it made me consider using an elbow instead.

    Thanks!

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    Retired Defense Industry Engineer jadnashua's Avatar
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    The toilet and sink won't benefit from 3/4" pex, but the tub/shower will (at least filling the tub, if you only have one showerhead, it won't make much of any difference when showering). Depending on the type of pex you use, and the diameter, they each have different minimum bend radii, with type-A pex being the most flexible. The type reflects the manufacturing method (there are three types -A, -B, and -C, with -B and -C being less flexible). It also depends on the temperature of the pex when you try to bend it and whether you're going against how it was coiled in the roll or not. A bend support for one brand may be too sharp of a curve for a different brand's pex depending on the type.

    Avoid extra fittings when possible. If the space within one stud bay requires it to be too tight of a bend, and you can run the supply in the next one over, you can usually avoid that sharp bend by using the whole bay next to it, then go straight into where you need it. Also, do NOT use pex AFTER the shower valve for the tub spout or you'll likely run into problems. Do that in copper or brass.
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Member lemmy's Avatar
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    It was about 75 degrees and it was being bent in the same direction as the coil was wound. It was Sharkbite brand so I assume that is PEX-B. The 90 degree metal pipe support was also SharkBite brand and purchased at the same place.

    I will have a shower head and a tub spout. What kind of problems are caused by running pex from the valve to the spout?
    Last edited by lemmy; 09-04-2013 at 11:05 AM.

  4. #4
    Forum Admin, Expert Plumber Terry's Avatar
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    What kind of problems are caused by running pex from the valve to the spout?
    All kinds of problems!

    All faucet manufacturers warn against it.
    It forces water out of the shower head while filling the tub. Run either full size 1/2" copper or full size 1/2" pipe nipples and fittings for the tub spout. PEX is undersized, and PEX fittings are even more undersized.

    If I'm supplying a bathroom with PEX, I run 3/4" cold and 1/2" hot.
    I can run two fixtures with 1/2"
    You can always go bigger too.
    Last edited by Terry; 09-04-2013 at 11:49 AM.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    WHen you use pex for the spout, it acts like a faulty diverter and allows water to rise up the shower head riser because it can't all get out to the spout opening. You REALLY need full sized piping to the spout...you could probably get away with pex up the riser, but NOT to the spout.
    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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    DIY Member lemmy's Avatar
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    Ok, that makes sense. Is 1/2" copper down to the tub spout ok or should it be 3/4 copper.

    This tub will just have one shower head and one spout. Actually it will have a detachable sprayer but that will not be on the same time as the shower head. Terry, so why do you run 3/4 cold and only 1/2 for hot? Is that just so you get the hot water more quickly?

    I need to cut in to an existing 1/2" copper line to go over to the shower. I was intending on using one of those push on slip fit tees, but I am not sure they make one that is 1/2 on the ends and the tee part that branches off is 3/4".

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    In the Trades Gary Swart's Avatar
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    Not to your question, but why in God's name to you want to use Pex in as system that is already plumbed with the best material already? Are you unwilling to learn to sweat a copper joint? Pex may have it's place, but I sure would use it for your job. End of rant, do what you want.

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    DIY Member jadziedzic's Avatar
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    Give this man a cigar (if he smokes)! Other than "cheap" and "fast to throw together", the only advantage I can see with Pex is using it in a home in a remote location that might be susceptible to freezing (e.g., a vacation home). Why hack in a "few feet of trouble"?

    Quote Originally Posted by Gary Swart View Post
    Not to your question, but why in God's name to you want to use Pex in as system that is already plumbed with the best material already? Are you unwilling to learn to sweat a copper joint? Pex may have it's place, but I sure would use it for your job. End of rant, do what you want.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Most all tub spouts are designed for 1/2" pipe. There may be some super quick fill commercial spouts with bigger openings, but I doubt you have one...IOW, 1/2" copper or brass nipples and fittings are fine for the tub spout, just not pex!
    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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    DIY Member lemmy's Avatar
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    So is your recommendation based on an emotional attachment to the way you have always done it or is it based on increased rates of failures with PEX plumbing or possible some sort of health/safety issue? If it is one of the latter then I would appreciate a link to any information issues with PEX or any personal experience.
    Last edited by lemmy; 09-04-2013 at 02:02 PM.

  11. #11
    DIY Member lemmy's Avatar
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    Quote Originally Posted by jadnashua View Post
    Most all tub spouts are designed for 1/2" pipe. There may be some super quick fill commercial spouts with bigger openings, but I doubt you have one...IOW, 1/2" copper or brass nipples and fittings are fine for the tub spout, just not pex!
    Thanks so much for your help.

  12. #12

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    Depending on what type of pex joining method you use, the water pressure will be affected. I run pex often and have never had a problem with it. I always use the expander method (uses white rings expanded with a special hand held power tool).

    The crimp method has a MUCH smaller fitting diameter compared to copper lines or the expander fittings for pex.
    Plumbing Professional
    Cahill Plumbing & Heating, Inc.
    Westborough, MA
    http://www.cahillplumbingandheating.com

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