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Radiant ceiling heating &cooling. Insulate under floor slab?

mercedes Member Posts: 65
Building a garage (28'x32'x10') in central Florida. Planning to do a radiant ceiling with heating and cooling. My question before I pour the new garage floor slab, should I place 2" foam insulation under the slab and edge perimeter or vapor barrier only? I will have the walls and ceiling insulated. Thank you again.


  • Dave Carpentier
    Dave Carpentier Member Posts: 171
    In Northern Ontario, heating is the bigger challenge, so insulation under is a good idea.
    My completely uneducated thought wrt Florida, cooling would be the bigger challenge, so leave the slab able to 'connect' to mother nature underneath and not insulate it.

    The question I have is.. if you chill the ceiling in a Florida enviro, would it not just rain condensation inside the garage ? I've never lived anywhere that hot, so Im just guessing..

    30+ yrs in telecom outside plant.
    Currently in building maintenance.
  • pedmec
    pedmec Member Posts: 191
    You have to run the chilled water above the dew point of the air, whatever that is. That's how they do it with chilled beam cooling
  • Tim_D
    Tim_D Member Posts: 70
    Underslab insulation has no benefit in your area and with your application but a vapor barrier is advised. Radiant cooling is a challenge unless you can control the latent load through another means. The radiant cooled ceiling will only handle the sensible load. You can get 2btu/sqft per degree of difference between the surface temperature and the ambient temperature provided that you dew point is low enough, usually under 40% rh.
  • mercedes
    mercedes Member Posts: 65
    Thank you all for the advice will make sure I have the dew point controlled and the vapor barrier under the slab.
  • Can't you take care of dew point condensation with a dehumidifier?
    Often wrong, never in doubt.
  • pedmec
    pedmec Member Posts: 191
    now what do you do with the latent heat that you just removed and is being converting to sensible heat? got to be able to dump it outdoors
  • hot_rod
    hot_rod Member Posts: 16,286
    Desiccant wheels can remove moisture also.

    When the slab gets warmer or cooler than the ground below, energy will transfer, hot to cold. Insulation is used to slow the transfer, save energy costs
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream