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Thread: Type M Cu For Hot/Cold Water Lines Question

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  1. #1

    Default Type M Cu For Hot/Cold Water Lines Question


    Live in a 35 year old house outside of Boston.

    Had a leak in a Copper water pipe that the plumber finally found.

    Unfortunately, I forgot to ask him if it was in a hot or cold line, as this might, perhaps, be meaningful ?

    Anyway, what surprised me was that it was pinhole leak in the middle of a run.
    Not at a joint or fitting, etc. Right in the middle of a line.

    Apparently they used the thinnest Copper they could find when they built the place.

    I used a caliper on it, and found it to be 0.028, which I guess is a grade M. (outside diameter of 5/8 inch)

    But, it still should take the household pressure without any problem, I would think. True ?

    The plumber replaced it with heavier wall stuff of approx. 0.038, which is probablyType L


    a. 35 years ago, was this (Type M) a "very common" Copper gage they used for household hot and cold water lines ?

    b. Is it still allowed, or the Codes prohibits it now all over ?

    c. What might make a pinhole leake in the middle of a clear run ?
    I guess the pinhole can be considered as a corrosion type of breakthrough.

    d. How common is something like this is the thinwall Type M tubing ? What causes ?

    Any thoughts on this would be most appreciated.


  2. #2
    Master Plumber nhmaster's Avatar
    Join Date
    Jul 2008
    S. Maine


    IPC and UPC both allow it's use but many states have adopeted an ammendment making illegal except for heating pipes. Most of us use type L.

  3. #3
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona

    Default copper

    I have not used type "L" copper in a residence, EVER. "M" has always been the standard.

  4. #4
    Plumber jimbo's Avatar
    Join Date
    Aug 2004
    San Diego


    You might want to investigate your water chemistry. Also water velocity and flow, like on a pumped recirc line, or a small line feeding a large demand, can cause erosion.

  5. #5
    In the Trades Gary Swart's Avatar
    Join Date
    Sep 2004
    Yakima WA


    I believe type M is still the standard. There may be some local codes or issues that specify type L.

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    The OD on copper like this is the same so any fitting will work (same with pex)...it is only the ID that changes with the wall thickness.
    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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