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Radiant Heat Loop

Hello, I have a boiler with multiple zone valves that feed radiators with one main circulation pump on the supply side of my boiler. I added a radiant loop with a mixing valve with an additional zone valve. My question is, do I need a separate circulating pump on the mixed side of the mixing valve that feeds my radiant loop?


  • Dave Carpentier
    Dave Carpentier Member Posts: 410
    Possible to make a sketch or post some photos ?
    30+ yrs in telecom outside plant.
    Currently in building maintenance.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 4,913
    YES. You need to get the mixed water to flow out of the mixing valve. The system pump can't do that.

    I have also found that you probably didn't need the zone valve. I did the same thing 20 years ago. Had a zone valve for future use when I installed my Buderus Boiler. 2 years later I installed some radiant floor heat with a mixing valve and pump. About 10 years ago I had a Zone valve failure and used the radiant zone to fix the problem temporarily. Turns out the thermostat operates the pump and heats the radiant room. When the circulator is off the room heat stops. So I never put the replacement head back on that zone. Still on the shelf for future use.
    Edward Young Retired HVAC Contractor & HYDRONICIAN Services first oil burner at age 16 P/T trainer for EH-CC.org
  • rmorrisjr24
    rmorrisjr24 Member Posts: 3
    Here is drawing, it’s a little crude, but should give the info needed.
  • neilc
    neilc Member Posts: 2,084
    yes, you need that pump there,
    known to beat dead horses
  • hot_rod
    hot_rod Member Posts: 18,190
    You need a pump, one with an integrated check valve, then you would not need the zone valve
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • rmorrisjr24
    rmorrisjr24 Member Posts: 3
    Thanks guys!