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Single Pipe Feed

Hello, I am new to this forum. Have some questions for a piping lay out for a radiant heating system.  Keep in mind this is a very old house with a very old wood/gas fired boiler 750,000btu(was moved here from another farm) and way over sized and system was not piped properly to begin with. So I am installing a new Dunkirk DXL-120K boiler. The house is plumbed with radiant floor heat in 1 part of the house and
baseboard/radiators in the other portion of the house. 1 thermostat controls radiators 1 thermostat controls radiant floor heat. The problem comes in that there is only 1 supply line from boiler to both systems it tees somewhere that cannot be located, but 2 returns coming back. 1 return for radiators, 1 return for floor heat. Never have ran into a single feed with two returns. We know it was never right from the beginning and cannot be piped correctly in the floor or walls now as it’s a entire concrete building and floor. My biggest issue is how is it possible to keep a low temp loop for the floor heat and a high temp loop for the radiators/baseboard with only 1 supply and 2 returns. If anyone has any input or any drawings would be great. My original plan was a primary boiler loop, a low temp secondary loop with mixing valve for the floor heat and a high temp loop for radiators. Not sure what’s the best option here to maintain some life in the new boiler and system until building is tore down In a few years.  Appreciate any help or input. Thank you. 


  • Jamie Hall
    Jamie Hall Member Posts: 23,428
    This depends a LOT on how that floor loop is piped in the floor. If the thing starts at one side and wiggles around and then ends over on the opposite side it won't work. But -- if it is multiple parallel loops, or if it goes out and over to the other side and then comes back to near where it began, you could try throttling the return. It will still be much too hot at the beginning, but by reducing the flow you can get the return much cooler.

    If it's a simple minded design and starts on one side and wends its way to the other, though -- as I say, that idea just won't work. One side will be much too hot -- and the other too cold.

    Another ply which might work would be to only let it flow sometimes, not all the time. Perhaps just long enough so that the return warms up. Still have the side to side problem, but it might not be as bad.

    The problem with just recycling the return is that it will also cool the radiator loop -- and you don't want that.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • hot_rod
    hot_rod Member Posts: 22,254
    Some of the retrofit radiant underfloor systems need to run at high temperatures. UltraFin, suspended tube, staple up without aluminum plates. How is the radiant installed?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • cwurst88
    cwurst88 Member Posts: 3
    Appreciate your response. My only other thought was to basically use a primary loop for the supply and install return pumps with a zone valve on Each return back to the primary loop and balancing valves(circuit setters). At least at that point when 1 or the other calls it won’t flow thru the opposite heating it up since the zone valves and return pump on the zone not calling will be off. 
    EBEBRATT-Ed Member Posts: 15,613
    Can;t say without x-ray vision. you need tp come up with a simple sketch of how it's piped so we an figure out what to do. first thing is what @hot_rod said. what kind of radiant system is it?
  • cwurst88
    cwurst88 Member Posts: 3
    The radiant is actually thru the pre cast concrete. It’s a old barn house that was built with all precast concrete.