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Thread: copper pipe support and thermal expansion

  1. #1
    DIY Junior Member old_man's Avatar
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    Default copper pipe support and thermal expansion

    Folks,
    I will be replacing a 20' section of 1/2" Cu that feeds external hose bibb (pinhole leaks). I am concerned about the lack of accomodation for thermal expansion of this long pipe. I looked up some formulas for expansion of copper tubing and how long pipe offset should be to accomodate expansion. (Technical Reference Guide Thermal Pipe Expansion) I figure pipe temperature can go as high as 85 degrees F (summertime, we are on vacation and have AC set warm and pipes are empty because inside value is off), and as low as 45 degrees F (winter). For a 20' pipe this would be an expansion of 0.082". This means that I need 19" between the 90 degree bend (at the end of the 20' length) and the next anchor point (according to above reference).
    1 - the current plumbing has only 6 inches of length (I'm thinking I need to increase it).
    2 - reading this forum as well as others there seems be a code requirement to support pipe within 12" of major change in direction. What happens if the need to accomodate expansion requires more than 12"
    3 - The references also describe that on each straight section there should be a single anchor point and additional supports should be "guides" that allow pipe to slide as the pipe expands. The 20' pipe is currently anchored firmly to a joist every 6' with a strap. Since the hose bibb itself is an anchor point on outside of house, seems like all interior supports on this 20' section should allow sliding.

    Am I overanalyzing this in my ignorance? Is there a more appropriate reference for this?


    Thanks.

  2. #2
    Forum Admin, Expert Plumber Terry's Avatar
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    The UPC mentions expansion on hot water lines, not cold water.

    Copper should be supported at least every six feet.
    You can use plastic j-hooks or snails, these allow pipe movement.

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    Moderator & Master Plumber hj's Avatar
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    With cold water, you will either have NO expansion, or very little, and NEVER 19" even with hot water.

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    DIY Junior Member old_man's Avatar
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    Quote Originally Posted by hj View Post
    With cold water, you will either have NO expansion, or very little, and NEVER 19" even with hot water.
    HJ,
    My calculated expansion is not 19", it is 0.082". The reference says that I need a 19" offset in order to accomodate an expansion of 0.082". By offset they mean the distance from the 90 degree fitting at end of long pipe and the next anchor point. In other words this 19" section will be flexing a few degrees in angle as the long pipe expands/contracts.
    I guess my concern was that this particular pipe does not always have cold water in it. I will be shut off every winter and may be left empty all summer if no one uses external bibb.

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    DIY Junior Member old_man's Avatar
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    Rechecked my figures using another reference (Copper Tube Handbook) and realized that I had calculated for 1" pipe (dammit). For 1/4" pipe the required offset length is only 8" for a 20' pipe with 20 degree temp delta). This is now very doable for me and complies with requirement for support within 12" of change in pipe direction.
    I now have these formulas in a spreadsheet which I am sure I will never need again.
    Thanks for the inputs.

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    Moderator & Master Plumber hj's Avatar
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    You aren't using 1/4" pipe EITHER, are you? Forget about those dimensions. They mean absolutely NOTHING in your set up. .082" is about 1/12" and you would have a hard time MEASURING that amount of expansion, much less compensating for it.

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    DIY Junior Member old_man's Avatar
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    Quote Originally Posted by hj View Post
    You aren't using 1/4" pipe EITHER, are you? Forget about those dimensions. They mean absolutely NOTHING in your set up. .082" is about 1/12" and you would have a hard time MEASURING that amount of expansion, much less compensating for it.
    HJ,
    Sorry man, I meant 1/2". I originally calculated incorrectly for 1".

    Thanks for allaying my concerns.

    Just curious though, Terry's earlier post indicated that the UPC code talks about expansion on hot water lines.
    If I have a 10 foot hot water line whose temp can go from 50F to 130F that is only 0.082" of expansion.
    At what point would you start worrying about expansion of a hot water line?

  8. #8
    Moderator & Master Plumber hj's Avatar
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    Seldom anywhere in a residential system. The only time expansion becomes a problem is when the tubing is secured aLMOST tight by a tight hole or a strap. Then it can rub in the restriction causing the "ticking" sound some think is caused by a leak. Expansion while heating up is rapid so the loudest sound occurs then, but it also happens while the pipe is cooling and contracting, but since that is a slower process it is not as evident.

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