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Adding underfloor radiant

I currently have hot water baseboard heat using a Navien boiler (having a circulator) feeding 4 relatively short zones in our one floor + basement house just built. The four zones are fed by 3/4" pex and another circulator and are : 1. Bed1 and basement 2. Bed2 and Bath 3: Living Room 4;DHW. I am planning to add underfloor radiant using the basement ceiling. For this I will use 1/2" pex. I would like to add the 1/2" pex to one of the four existing loops (up to 300') and I am wondering if such a plan would be manageable by the circulators or will I need another circulator and use a completely separate loop for the underfloor.
Thank you


  • Jamie Hall
    Jamie Hall Member Posts: 23,635
    The problem isn't the circulator so much as the temperature. Depending on the circulator, you may or may not get much flow in the radiant piping, though this could be corrected with balancing valves (at which point you may or may not get enough flow in the baseboards...).


    Radiant floors run at a much lower temperature than baseboards do, at least under higher load conditions. You might, possibly, with very good luck, get away with running the radiant as the end of a series loop with the baseboards in that zone. Probably not.

    The radiant should have it's own zone, with a temperature regulating or mixing valve to control it's temperature (a form of primary/secondary piping), which means -- among other things -- another pump (or circulator... whatever) in there somewhere.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    JUGHNE Member Posts: 11,102
    If your BB is running at the typical high temp of 140-180, you need lower temp for the underfloor pex.
  • abineri
    abineri Member Posts: 3
    If the boiler is set for a high temp o 140, might is not be cool enough, at the end of a run to send it underfloor?
  • Big Ed_4
    Big Ed_4 Member Posts: 2,827
    Radiant is another animal , Separate circulator , mixing valve and a floor sensor . Break the loops down for more even heat . Wood floors above hook up the outdoor sensor and maintain humidity .

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  • hot_rod
    hot_rod Member Posts: 22,468
    One way to use the same high temperature would be the Ultra Fin system. Suspended pex with clamp on aluminum fins. 
    Be good to do a load calculation first to see what the rooms require for Btu/ sq. Ft,
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream