Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Calculating manifold headloss

If I am running multiple 1/2" PEX lines from a manifold is the total headloss the sum of all the loops? Or is it more complicated than that?


  • Gordy
    Gordy Member Posts: 9,546
    edited December 2010

    Would be the LONGEST loop in that manifold. Plus the supply, and return headloss.

  • yellowpit
    yellowpit Member Posts: 2
    Thank you.

    That's easy.
  • Ironman
    Ironman Member Posts: 7,376

    However, GPM is the sum off all the loops, but is calcuated based on btu's and temp drop through the radiation.

    In other words, what's the calculated btu loss for the area served? Once you know that, use this formula to determine the needed GPM:

    Btu = 500 x Delta T x GPM.

     Example: You should have a 10 deg Delta T for radiant floors. Let's say your heat loss is 15,000 btu's. 500 is a constant for water.  15,000 / (500 x 10) = 3 GPM.

    The 3gpm should then be balanced between the number of loops in the floor.

    If you're using radiators, the Delta T should be 20 deg. but the GPM should be determined individually for each rad based on its btu rating. Use the same formula to calculate each rad and then the sum GPM to determine the pump size for all connected to that manifold. Adjust each loop on the manifold to give whatever gpm is required to each individual rad.

    A radiant floor can be balanced equally because it's basically just one emitter (radiator).
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
This discussion has been closed.