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Thread: PEX in an exterior wall

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    DIY Senior Member Noth Jersey's Avatar
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    Default PEX in an exterior wall

    How should I insulate PEX tubing I intend to run through my exterior walls? I will place the PEX on the warm side of rigid foam insulation, but I imagine I should also use split foam insulation to prevent condensation. Building an interior partition just to conceal the PEX is not really an option at this point.

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    DIY Member edlentz's Avatar
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    Well, I'll tell you I had the same delemma (sp?) I had to run lines into an outside wall for a kitchen sink instead of going through the floor to the basement. I ran copper to a set of valves and used sharkbites to connect the pex. A nice sweep into the wall up about 20" to a copper 90 and out to the sink shutoffs. I put insulation between the outside wall and the pex. I figured PEX would hold up to freezing better than copper, since the pex will flex and the copper won't. I live in Michigan and we've had some cold weather this year!

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    Quote Originally Posted by edlentz View Post
    Well, I'll tell you I had the same delemma (sp?) I had to run lines into an outside wall for a kitchen sink instead of going through the floor to the basement. I ran copper to a set of valves and used sharkbites to connect the pex. A nice sweep into the wall up about 20" to a copper 90 and out to the sink shutoffs. I put insulation between the outside wall and the pex. I figured PEX would hold up to freezing better than copper, since the pex will flex and the copper won't. I live in Michigan and we've had some cold weather this year!
    What type of insulation did you use? Did you insulate with foam tubing for the condensation? So, you haven't had anything freeze? I imagine you've had temperatures a lot colder than ours.

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    Forum Admin, Expert Plumber Terry's Avatar
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    PEX doesn't sweat.

    You can even bundle it, and the hot won't cross over to the cold either.

    Uponor PEX plumbing systems retain more heat in hot-water lines and resist condensation on cold-water lines.
    Uponor web site
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    Last edited by Terry; 01-27-2009 at 03:28 PM.

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    DIY Senior Member Noth Jersey's Avatar
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    Quote Originally Posted by Terry View Post
    PEX doesn't sweat.

    You can even bundle it, and the hot won't cross over to the cold either.
    Great news. We have fairly cold groundwater, so I was worried about the temperature differential in the winter. Good to hear about the bundling, too. That knowledge should simplify this project considerably. Thanks for the input.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Unless there's air movement in the wall, there normally wouldn't be much moisture to condense. Now, after exiting the wall, all bets are off. But, pex IS a poor conductor.
    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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    Master Plumber nhmaster's Avatar
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    If you go ahead and install it in an outside wall and it does happen to freeze, getting it thawed out is a huge PITA.

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    DIY Member edlentz's Avatar
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    As for insulation I just used r13 fiberglass as I remember. This is the first winter so over the long haul we will see. Although I am pretty certain the pex will hold up over time. If the heat won't migrate from the inside out then the cold shouldn't either, right? Time will tell if I was wrong or not

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    Quote Originally Posted by Terry View Post
    PEX doesn't sweat.

    You can even bundle it, and the hot won't cross over to the cold either.
    So the Wirsbo stuff I'm using should be more resistant to condensation than run of the mill PEX?

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    Quote Originally Posted by nhmaster View Post
    If you go ahead and install it in an outside wall and it does happen to freeze, getting it thawed out is a huge PITA.
    Yeah, I'm not sure I would want to string heat tape along every run. Hopefully the 1/2" drywall will not insulate the wall cavity to the point at which the PEX freezes. If the old copper running along the rim joist doesn't freeze (except for a pipe I discovered on the cold side of the insulation), should I anticipate frequent problems with the PEX?

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    DIY Senior Member Noth Jersey's Avatar
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    Quote Originally Posted by edlentz View Post
    As for insulation I just used r13 fiberglass as I remember. This is the first winter so over the long haul we will see. Although I am pretty certain the pex will hold up over time. If the heat won't migrate from the inside out then the cold shouldn't either, right? Time will tell if I was wrong or not
    What kind of temperatures have you seen since you installed the PEX? At least I won't have to worry about having a river spring from the side of my house like when a sweat fitting on the outside of my insulation burst. We are using two 1500 watt space heaters to heat the main floor while I work on putting in our mini split for the main floor, so the basement didn't weather the record-setting cold temperatures well.

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    DIY Member edlentz's Avatar
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    Well, when I went to work this morning the outside temp was 0. We have had many of those and lower nights this winter. I should mention that the pex I have is from the DIY orange box. Some of the stuff they sell in short lengths. Nothing special. It is routed between the two rim joists and into the wall cavity, and out to the sink. I have seen stories how the pex is filled with water and sealed, and frozen all without bursting. That cinched it for me.

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