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Radiant Heating and Flow rates??

KungurKungur Member Posts: 49
As I proceed with my radiant heating retro project I have a question I hope someone here can help me with. I am installing the pex in my basement up against the 1st. floor subfloor. I will have 11-12 loops. I have the rough length of each loop calculated. What I am trying to determine is how many manifolds to use. And how to figure out the flow rate so I know how many circulators.

Would appreciate your assistance!


  • CMadatMeCMadatMe Member Posts: 3,066
    edited August 2010
    Loop Lengths

    I want to make sure my loops are even across my manifolds. I also remote my manifolds. So to anwser your question is impossible. Not enough information. Have no clue to the floor layout and how many zones (not manifolds) you are doing.

    I never do joist heating without plate unless I am doing just floor warming and I always use 3/8" pex. No advantage to using 1/2" and 3/8" is a heck of alot easier to pull.  My loops lengths are what my radiant heat loss/design calls for but I like to keep them no longer than in the 200' range plus or minus 10 feet. Pretty much any basic residential circulator  (007) or equiv will take care of the job. Head is not cumalative. If the pump can overcome the highest it can overcome everything?

    Whose Pex did you use? Where did you get it? You should be able to go back to the place you purchased the tubing and ask for that manufactures chart to calculate head. The flow rate is dependent on the radiant heat loss.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • NRT_RobNRT_Rob Member Posts: 1,009
    you need

    you be able to calculate flow rates and heat loads to answer your questions. If you can't, then you'll want help.

    I do not worry about equal loop lengths as long as you have flow meters/balancing valves on the loops. Assuming you have multiple rooms on the system pump, that should pretty much be a given as far as I'm concerned.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
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