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Radiant Heating Pipe Size Assistance

Good evening,

I'm remodeling a home in central WI and have a boiler system with aluminum fin tube baseboards on copper pipe. Ranch style, two zones; main floor & basement. Since I've taken all the walls down to studs and put drywall up, I'm having to move all the registers to get them in the right position. I've also decided I'm going to replace the current copper pipe with Pex-A tubing (I'm passable on sweating copper, better with PEX). I measured the current pipe at nearly 15/16" OD and over 3/4" ID and was planning on putting 3/4" PEX. I guess I just need some reassurance that I'm replacing the old stuff with the right size pex. I'm sure there is flow rates and heat loss calculations but i'm just following the current path to replace and only moving a few registers so I figure I just need to replace with the right size to maintain integrity of the originally designed system.



  • Jamie Hall
    Jamie Hall Member Posts: 23,270
    3/4 PEX should work fine
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Zman
    Zman Member Posts: 7,569
    I agree, 3/4" will work fine unless your lengths are really long.
    Be sure to use a pex tubing with an O2 barrier. Uphoner Hepex is popular pex-a with barrier.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    EBEBRATT-Ed Member Posts: 15,510

    FWIW The tubing you measured is actually 7/8" od which is 3/4 nominal copper tubing. In AC & Refrigeration the same size is called 7/8 OD copper tubing.

    Welcome to the world of the American misfit measuring system. All kinds of confusion