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Radiant Heat

RayH Member Posts: 90
edited December 2018 in Oil Heating
This is new residential home under construction in Maine. I want to do the initial start up on radiant heat in a frozen slab. The builder wants the heat turned on in the slab only. The 3 other hot water baseboard zones are not ready yet. I want to introduce glycol into the loops. The well water is not turned on because of possible freezing. Any ideas ?


  • DZoro
    DZoro Member Posts: 1,048
    Suggest temporary forced air heat until concrete is at least warmed up above freezing. When you do finally start the slab warm up go slow, very slow. Use very low water temps and bring them up on a daily basis. Take your time, keeping the temp. forced air heat on.
    The post is in oil heat, is that going to be the fuel?
  • GroundUp
    GroundUp Member Posts: 1,758
    I have a radiant hat also, it keeps my noggin warm. But also, what concentration glycol do you intend to fill with and what is the temperature of the slab? Assuming the freezing point of the solution is lower than the slab temp, what is the issue? Pump it in premixed as you should and purge as normal with transfer pump (or whatever you like to use) and begin system circulation using very low water temps, slowly mixing up to operating temp. Done deal
  • Jamie Hall
    Jamie Hall Member Posts: 22,162
    As said above. Go slow. Very very slow, with as low temperatures as you can manage. The risk is differential heating of the slab, which will crack it. Were it mine, i'd go with @DZoro 's suggestion: forced air until the slab is above freezing (use one or two of the lovely propane dragons -- they work great).
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • nibs
    nibs Member Posts: 500
    How thick is the slab?
    Can you find out the design mix of the slab.
    Does the slab have fiber entrained?
    How long has the slab been curing?
    Absent an infloor sensor, if you lay a thermometer on the floor and cover it with a good layer of insulation and a blanket, you can find the temp of the slab. You may be surprised at the actual temp of the slab, and use that to govern your actions.

  • Gordy
    Gordy Member Posts: 9,537
    When you think about it. Snowmelt is about the same stress on a slab of concrete. The btus will be sucked up like a sponge.
  • nibs
    nibs Member Posts: 500
    It costs very little extra to make cement much stronger that the standard 3500 psi mixes.
    As long as the slab is not a very thin slab of weak concrete, there should not be too much worry, biggest danger would be the water freezing in the slab piping.
    Get your builders to add fiber to the cement and to use super plasticizer to reduce water content.
  • Gordy
    Gordy Member Posts: 9,537
    edited December 2018
    Good luck with the super P on a residential job :D . Why do I need that when I can just add water :p matter of fact calcium chloride will be on the list before super this time of Year......
  • GroundUp
    GroundUp Member Posts: 1,758
    Gordy said:

    When you think about it. Snowmelt is about the same stress on a slab of concrete. The btus will be sucked up like a sponge.

    I wasn't going to make any recommendations, but I abuse the crap out of my sidewalk snowmelt at home with nary a crack after 4 years. It was mostly a guinea pig to see what they'll take, so on multiple occasions I've pumped 150 degree water into a -20 degree slab and it still looks perfect. I prefer to abuse my own stuff instead of experimenting with customer projects