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Community and Q&A

Garage with in-floor heat

Pokegama | Posted in General Questions on

I live in a northern climate where freezing temps and snow is a common occurrence during the winter months. I am planning to build a new garage using hot water in floor heat. I was told by the plumbing contractor that in floor heat is not advisable unless a ventilation system is installed as well. Along with floor drains. The reason for the ventilation system is to guard against mold growing in the insulated walls caused by the evaporation of water from snow melting off the vehicles. Apparently the water is partially absorbed into the concrete and this heated moisture is transferred to the wall spaces where mold can accumulate. Only constant ventilation will remove this excess moisture. Obviously venting out heated air somewhat defeats the purpose of heating a garage when it’s 30 below and certainly not very energy efficient. The contractors claim seems logical but I have not been able to find any research on this subject and wonder if he is just trying to sell me a ventilation system on top of the in floor heat. Wondering if anyone has run into this problem or if there is any valid studies done that I could review.

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  1. cabinflyer | | #1

    With the garage door and all the leaks associated with it, I'm doubting your garage will be as airtight as a well insulated home. I put in-floor heat in my 26x28 garage and have no mold issues. With that being said I wouldn't put in-floor heat in a garage again. Too expensive to keep heated, even with Lake Country dual fuel credits. You might consider a sand storage type system to take advantage of off peak rates.

  2. user-2310254 | | #2


    Is your slab insulated?

  3. Jon_R | | #3

    My guess is that good floor drains and floor slope, epoxy coated concrete, < 50F, polyethylene on the walls (and under the slab) and the inadvertent ventilation from the garage door would be plenty to prevent mold growth in the walls.

    One can always add ventilation(preferably a HRV) if it doesn't.

  4. GBA Editor
    Martin Holladay | | #4

    I agree with Steve and Jon: I think that your garage will get enough incidental air leakage to prevent mold in your walls. In you ever discover in the future that a ventilation system is needed, it will be easy enough to install a ventilation system at that point.

    The most important details for this type of installation are (a) an adequate amount of vertical rigid foam insulation at the slab's perimeter, and (b) an adequate amount of continuous horizontal rigid foam under the entire slab. In a cold climate, a heated slab needs a minimum of 4 inches of rigid foam in both locations.

  5. Jon_R | | #5

    It would be interesting to explore more energy efficient alternatives. Perhaps engine block heaters, radiant heating used only when working in it, passive solar, heating only to 10F, etc.

    I'm considering "Green Hinges" to improve the air sealing (trying to reduce rust).

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