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pipe size reduction - will it affect radiator heat

redcar383 Member Posts: 2
My basement has cast iron hot water heating pipes. In order to remodel my basement these will have to be moved much closer to the walls. Question - I have a number of feeds of 3/4" off of the 1" main runs. In using Pex rated heat pipe and fittings I have to go to 1/2 heat pipe pex for the threads to match up. Will this affect the radiant heat output of the radiators?

Thank you


  • EYoder
    EYoder Member Posts: 60
    Are these cast iron radiators or baseboard? 1/2" pex can handle a good size cast rad if each is piped individually.
  • SuperJ
    SuperJ Member Posts: 609
    If you pipe your rads in parallel you'll likely be fine with 1/2" pex. But if you can post some more specifics about your system you'll get better feedback, like rad size/output, pipe runs, water temp, etc.
    Pictures are good too.
  • Ironman
    Ironman Member Posts: 7,379
    The piping in your system was carefully balanced when it was installed - particularly if it was originally gravity flow. If you change part of it, that will throw it out of balance.

    Water takes the path of least resistance. While 1/2" may carry enough flow if the entire system was designed for it, it will most certainly be too small if the other rad's have larger piping.

    What I'm saying is that the system must be viewed as a whole in designing and selecting pipe sizes. You can't just redo the pipe size of only part of it. That's why more info is needed.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • redcar383
    redcar383 Member Posts: 2
    Thank you! Bob, Superj and Eyoder.. I (may) have enough information at this point..
    with sincerely very much thanks Gentlemen
  • Tinman
    Tinman Member Posts: 2,808
    Run a 1/2" Pex-Al-Pex supply and return from each radiator back to the boiler room and connect them to manifolds with flow meters and balancing valves. I.e. Homerun manifold distribution system.
    Steve Minnich