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Thread: Using CPVC at the boiler?

  1. #1
    DIY Member jimmym's Avatar
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    Default Using CPVC at the boiler?

    After some recent work, I have a question.
    I replaced all my copper with CPVC (100PSI @ 180F). Except at the boiler.
    I went from CPVC to copper then went to the thermal trap, DHW coil and the cold side of the tempering valve, then another thermal trap. Only then did I go back to CPVC.
    My question is... Why bother? Couldn't I have just used CPVC for the whole thing? My boiler runs at 180F and water pressure in my house is about 50 PSI. As it is now the CPVC pipe will never see temps above the tempering valve setting.
    Any thoughts?

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    Plumber jimbo's Avatar
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    Default

    It is not recommended to have any plastic pipe in direct contact with a water heater or boiler.

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    DIY Member jimmym's Avatar
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    Quote Originally Posted by jimbo
    It is not recommended to have any plastic pipe in direct contact with a water heater or boiler.
    "Direct Contact". So if I use a 4" copper stub from the boiler to the CPVC transition, that would be OK?

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    Moderator & Master Plumber hj's Avatar
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    Default cpvc

    You are assuming the tempering valve will never malfunction. That is not a very wise assumption.

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    DIY Member jimmym's Avatar
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    Quote Originally Posted by hj
    You are assuming the tempering valve will never malfunction. That is not a very wise assumption.
    Even if the tempering valve jams on full hot, that's only 180F, CPVC is rated to 100PSI @ 180F and is serviceable to 200-210F. I'm not seeing the real problem here. Domestic water pressure will only be about 60PSI.
    I suppose that if the pressure switch fails AND the pressure relief at the bladder tank fails AND the TPR valve fails AND the boiler high limit fails... then I might get 100PSI water at temps over 180F. That, I think, is the textbook definition of "statistically insignificant". I'll bet that more people are killed each year from electrocution because of lightning and copper pipes than experience the above listed simultaneous failures.

  6. #6

    Default Using CPVC at the boiler?

    I believe the CPVC is a good product, but I would be very hesitant to use it for ANY heating applications at least for three reasons:
    1.CPVC does not have any oxygen barrier and is permeable. Even if your boiler is fabricated from SS, you will induce numbers of other problems.
    2.Even if your system is bulletproof and always will work only at 180°F; I do not believe that the CVPC at that temperature will be structurally sound.
    3.The expansion ratio is totally different… heating system is cycling..you may see pretty soon some leaks; there is no much room for tightening..

    Best,
    Pavel

  7. #7
    Moderator & Master Plumber hj's Avatar
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    Default cpvc

    The only critical number is the temperature that the T&P valve will open at, and that is 200 degrees. If the temperature reaches that level, for any reason, your CPVC could fail. I would not be comfortable running CPVC at its maximum temperature and hope that I did not have a piece that was not up to specifications.

  8. #8
    DIY Member jimmym's Avatar
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    OK. I was talking about using CPVC at the boiler for DHW not hydronic water. I agree about the hydronic water temps.
    The DHW would only be as hot as boiler water when it came out of the DHW coil.
    I guess I'll just plumb with CPVC up to "near" the boiler, where my thermal traps begin. Then switch to copper for connections to and from the DHW coil and the tempering valve.

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