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Radiant system pump selection

I am trying to determine if my pump is sized correctly. I have an in slab system, 1/2” per 12” spacing. Each loop is 300’ with 8 loops. I am using a Rhani on demand water heater. The delta t is approx 70 deg F. Flow rate per loop is .4 gpm. I purchased 2 Taco 007-f5 pumps. One on the supply and one on the return.
I am thinking the pumps are too small to provide the proper flow to get a better delta T.
Inlet temp is 140 F outlet temp is 70 F.


  • Zman
    Zman Member Posts: 7,328
    edited January 2019
    We get at least one of these a week.
    The 007 would work just fine if you were piped primary/secondary as you should be.
    Hot water heaters are not boilers and will not last very long or perform very well in that application.
    If you post pictures and drawing, you will get more detailed advice.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • GroundUp
    GroundUp Member Posts: 1,398
    That's 112,000 BTU per hour dumped into the space which I can only assume is roughly 2400 sq ft. Is this space missing a wall or did someone forget to insulate? Your flow rate is actually pretty decent judging by the flow rate (if accurate) which would likely be raised a bit by P/S piping as the head loss through a tankless is stupid high. As for your delta, I'd be willing to bet if you turned the supply temp down to 100 or so, your delta would cut down to about 25 degrees and would run longer for a more even heat. That's just speculation of course, without some details on the building
  • cbarner69
    cbarner69 Member Posts: 2
    The building is 2400 sq ft with 14 ft ceiling. I insulated the ceiling but need to do the walls. I want to do spray foam insulation on the walls but have to wait for warmer weather. I will try the lower temp and see how that works.