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Use of Pex instead of copper in monoflow tee system

jay in NY
jay in NY Member Posts: 18
What would be the best type of PEX tubing to use for this application, boiler water from 160-190 deg temp? I was going to use 3/4 inch PEX for the runs from the manifolds to each radiator. Currently each rad is fed by 1/2 copper off the main 1 1/4 monoflow copper line.


  • jay in NY
    jay in NY Member Posts: 18
    Use of pex in place of copper in a monoflow T system

    I have a two story home that currently has a single monoflow loop that feeds cast iron radiators on both first and second floors. The existing loop is 1 1/4 inch copper. I want to add a second loop and separate the first floor radiators from the second floor. Is it possible to use PEX to feed monoflow tees to each of the 6 radiators present on the first level of the house? If so what hardware should I use? I want separate zones to control heating and save energy.

  • Norm Harvey
    Norm Harvey Member Posts: 684

    I would advise against PEX for a monoflow loop unless you oversized the PEX as the fittings restrict flow quite a bit.

    I understand PEX may be easier for a retro fit application, but I would use copper if it were my own house.
    "We see the world as WE are, not as IT is, because it is the "I" behind the EYE that does the seeing"
    EMC PLUMBING Member Posts: 22
    venturi system

    if your basement is unfinished,and you can reach all lines feeding rads. you might want to try running pex manifold right off your boiler with home runs to each rad. using pex, have done it and worked great.
  • monoflo pex

    I like the manifold idea. you can't use pex because you momoflo loop has to have a constant pitch back to the boiler
  • manifolds

    I would go with a manifold in the basement and run 1/2 fosta pex to each rad from an 1 1/4 manifold. I am a Viega guy some others will use Wirsbo or watts. Go with what is readily available to you. Look into an outdoor reset controler for your boiler also those temps are a little high for castiron rads.
    I would not use a monoflow system there is a preasure drop in the monoflow tees and the pex tees. The pump will be working to hard to over come the preasure drop.
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