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I have an external water heater in a contained closet with two copper pipes, 1", running up from under the house to the fittings, through the water heater, then back down again. Coming back home after the Texas cold snap they were split vertically in several places. I am not relishing going under the house in that mud and inspecting there!

I have a question from a physics standpoint:

  • Would the copper pipes have been the weak link in terms of bursting? I have never yet seen any of my metal/galvanized pipes do this, only PVC and (now) this copper.

It's an old house so the pipes are an amalgam.

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  • Copper is softer and thinner than steel so should split first. I am surprise about PVC splitting, usually that can expand enough to prevent. Steel and galvanized will and can split also if frozen. Do not think I had a frozen PVC/plastic pipe split. One reason I changed from steel/copper.
    – crip659
    Feb 18, 2021 at 0:02
  • @crip659 pvc shatters it breakers in all kinds of crazy patterns. The galvanized may also have split it all depends on how it froze I have seen galvanized close to the vents where the pipes froze split in the middle the copper closer to the bathroom must have been warmer than was ok
    – Ed Beal
    Feb 18, 2021 at 0:10
  • and to be honest the PVC may have had some UV exposure, and have been in a place where the ground swole and contracted.
    – Oliver Williams
    Feb 18, 2021 at 0:32
  • @Ed Beal probably right for PVC, usually just use the cheap black plastic pipe for frozen conditions(in barn).
    – crip659
    Feb 18, 2021 at 0:33
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    What practical problem are you trying to solve here? We're not the venue for hypothetical discussions. See diy.stackexchange.com/help/dont-ask.
    – isherwood
    Feb 18, 2021 at 15:49

1 Answer 1

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It is impractical to try to use pipe that is strong enough to resist the stress of freezing water. You need to insulate it and possible add heat like thermostatic controlled heat cable to prevent freezing . In smaller diameters Sch 120 steel will probably handle it , but very impractical

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    There is actually one type of pipe that resists freezing pretty well: PEX. It's not that it's strong enough; rather it's flexible enough to stretch without breaking when the water freezes, and shrink back down when it melts. This isn't a guarantee though, so heat tape or other winterizing is still recommended. But it should be less likely to burst than any standard rigid pipe.
    – Nate S.
    Feb 18, 2021 at 17:32
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    As an old metallurgist , I do not trust rubber/elastomer pipe. One of the two SS braid with elastomer pipes I installed on a water heater, leaked after less than 5 years .And when Amoco tested a bunch of FRP pipe the conclusion was it was good for about one third of manufacturers pressure rating . I am pretty sure they have been re-rated as a result.
    – blacksmith37
    Feb 18, 2021 at 20:45
  • What is the expected lifetime of all the elastomer lines being used for toilets, lavatories, kitchen sinks, clothes washers, dishwashers? Is the elastomer under the SS expected to have an indefinite service life?
    – Jim Stewart
    Jul 18, 2021 at 16:24
  • @NateS. - just FYI I generally agree with you but pex has issues with thawing and or excessive heats around the clamps/joins. If this thing freezes a few times there could be a leak in the joint eventually. Now if this is outside what the concern level is... is up to the owner. They are not foolproof for freezing. Now in Europe they use PVC to run water lines up north (sometimes). These handle freezing temps much better but again not 100%.
    – DMoore
    Nov 15, 2021 at 20:08

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