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Any reason a kickspace heater Monoflo system with 3/4 pex for both loops won't work?

Jells Member Posts: 576
I've taken a Monoflo loop of 3/4 pex off of copper 3/4 to feed a kickspace heater before, but is there any reason it won't work if the main loop is also 3/4 pex? I'm afraid the small diameter of 1/2 pex will create too much resistance for the Monoflo to work. My gut says less resistance on the heater loop the better, but then why do the Monoflo's always tee out a size smaller? Is it just material cost efficiency?


  • pedmec
    pedmec Member Posts: 994
    i would worry more about the pex fittings than the pipe. keep the pex fittings to a minimum. I pipe copper from the kickspace heater to below the floor and use copper 90 and the tie pex in on a straight run.

    And make sure you spread the tees apart. the 3/4 might work for you as its going to create a higher resistance between the tees than say 1 x 1/2 monoflo tee. you also could do two monoflo tees too. but its trial and error.

    Smaller branch is because you only need a portion of the flow to go threw the kickspace heater. if you have a k84 you need just under a gpm. the pressure drop thru those are less than you think as long as your not trying to jam all kinds of gpm. not much more heat gain with a higher gpm flow
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,157
    edited May 2022
    The design of a mono-flow system has to do with pressure drop that causes a portion of the water, flowing thru the main pipe, to divert to the branch circuit in order to feed the emitter. It is better explained in this booklet on page 22. http://media.blueridgecompany.com/documents/ZoningMadeEasy.pdf.

    This description was presented to describe why zone valve may not work on old existing mono-flow systems. If you are starting from scratch in your design, then as long as you calculate the pressure drops correctly, you could use 3/4 PEX for the branch. If you are designing by trial and error, then you may get lucky. The fact that you may not find 3/4 x 3/4 x 3/4 mono-flow tees is basically because that size would not fit the parameters of good system design, and therefor not be in demand. A manufacturer would not choose to manufacture a fitting that no one would ever purchase.

    You would need to use reducing couplings or bushings to accomplish your goal. Good luck with you design. let us know how it works out (if it does) or if it is a bad idea.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • Jells
    Jells Member Posts: 576
    Thanks @pedmec . I was going down through the floor into the joists and using wide turn copper ells.  I'm using 2 k120s and a Taco 006, I think the flow should be pretty good.