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Radiant in floor heating sizing boiler and circulator pump.

I have a 1500 square foot building with 6 loops at 250 ft per loop. I think it needs at least a 40000 boiler and a 6 home circulator pump but wanting a little more info rather than just guessing what size of pump and boiler to put in. Am I close at all?


  • GroundUp
    GroundUp Member Posts: 1,406
    What's a 6 home circulator pump? The full answer is that nobody knows how many BTU the building needs until a heat loss analysis is performed. A super well insulated slab on grade home with 9ft ceilings in Kentucky might only need 5 BTU per square foot on a design day. A drafty pole shed with 16ft sidewalls, huge doors and minimal insulation in Minnesota might require 80 BTU per square foot. "Average" construction of garage/shed space in my area of MN tend to end up usually 20-30 BTU/sq ft so 40k would serve the majority. Six 250ft loops of 1/2" pex at .6 GPM and a 20 degree delta T makes roughly 5ft of head and 36,000 BTU with 100 degree supply water (pretty typical with 12" tube spacing and a 4-5" slab) which is enough to keep a decently insulated building 70 degrees in most cases. Something like a Taco 007, Grundfos 15-58, B&G NRF 22 or 25- all would serve that slab well. I'm a Grundfos guy personally but there are plenty of options
  • Henry
    Henry Member Posts: 995
    We give the plan of the building to the radiant manufacturer. They decide on the loops, spacing and number. They give us the flow rate required per loop and total flow rate and head loss. We refuse to connect to any DYI install of tubing as the liability is to the contractor that hooked it up. I supposed and I think, are not ways to start a project.