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Putting in Radiant Heat

abqgaryabqgary Member Posts: 5
I currently have baseboard heat and would like to combine radiant heat off the return side. It would save a lot of issues with adding more zones, mixing valves and extra piping.
If I reduce the water temp to 160 on the supply side, will my PEX OB pipe work properly? Are there concerns of too much expansion with the higher temp?
Thanks, Gary


  • ZmanZman Member Posts: 5,737
    edited October 2019
    I am afraid it is more complicated than that. What type of boiler do you have and how is it piped?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • GroundUpGroundUp Member Posts: 960
    Too hot. Needs a means of dropping supply temp (mixing valve) to usually 90-120 degrees depending on the system. It's not a tubing issue nor expansion issue so much as proper heat distribution. Is this a slab or staple-up or what? Need some more details
  • mikeg2015mikeg2015 Member Posts: 1,178
    edited October 2019
    Not hard to add a mixing valve before the injection pump.... which you will need anyway to get the flow rates correct for hte radiant loop.

    IF everything else is on a direct primary loop, then this would be a secondary on the return after the baseboards. You’d use closely spaced tees, and again, a mixing valve to drop it to 90-120.

    The biggest challenge is that baseboard is low mass, and radiant is high mass, so except on the coldest days, it could struggle to get the floor warmed up, then once warm, you’ll have too much heat. Will have to play with flow rate and temp to get it all balanced.

    It will need ot be it’s own zone however. Baseboard runs at 2-3 CPH, radiant floor 1 CPH
  • Solid_Fuel_ManSolid_Fuel_Man Member Posts: 1,958
    We have no idea if it's a low or high mass radiant system. Staple up, would be fine at 160, slab would not!

    There are plenty of old staple up systems running as the same temps as fin-tube.
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • abqgaryabqgary Member Posts: 5
    It would be a staple up system and the gas boiler is 3 years old.
    What if I turned the temp down to 120 and put in a radiant heat system in conjunction with the baseboard heat? i would probably only use the baseboards below the windows.
  • abqgaryabqgary Member Posts: 5
    Thanks for your help. Sounds like a Ultra-Fin system would work for my application. Has anyone used this system before?
  • Solid_Fuel_ManSolid_Fuel_Man Member Posts: 1,958
    Ultra-fin works reasonably better than just plain staple up. Be sure to gap it below the subflooring and to insulate below it with something reflective.

    Likely 120 wont make much heat. What kind of gas boiler? Atmospheric, condensing?
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • abqgaryabqgary Member Posts: 5
    I have an atmospheric gas boiler. Using the Ultra Fin system, I can leave the boiler at current 170 degree levels and get the radiant heat I want.
  • We've used Ultra-Fin many times with excellent results, but usually at lower temperatures. Call them at (888) 565-2267 and ask about elevated temperatures.
    Often wrong, never in doubt.

    Click here to learn more about this contractor.
  • abqgaryabqgary Member Posts: 5
    OK, thanks. Can I leave the baseboard heat under the large windows in conjunction with the radiant heat? It will all be on the same zone and I do not want to overheat the room.
  • hot_rodhot_rod Member Posts: 13,196
    I think Ultra Fin can work across a wide temperature range They basically create or increase convection transfer in the joist bay Output would vary with temperature of course
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
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