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how to insulate hydronic heated floor over a crawlspace

WoodCarver75 | Posted in GBA Pro Help on

I live in southern Maine, Zone 5. My kitchen floor is about 250 sq ft and is over a crawl space about 2′ – 3′ high. The stone walls around the crawl space has been sprayed foamed. I have laid a 1/2″ tube hydronic radiant floor over the subfloor in a slab about 1.5″ thick. Right now the i am pumping water into the loop at about 81deg and the return is coming out about 71deg. the slab temp is only about 61degs. this has been running for over a week now. I did not insulate the underneath of the subfloor. I now believe i need to insulator under the sub floor. Here’s my questions.
Should I use a reflective foil against the subfloor than follow up with rigid insulation board? should I use a rigid insulation board with foil? will just one layer of 2″ rigid board be enough?

Prior to the pouring of the slab, I had batting underneath. but rodents would get in and tare it down. So i would like to prevent this.

Thanks for your comments

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  1. Jon_R | | #1

    The insulation will be slightly more effective with foil and a gap. Either way is OK.

    A semi-conditioned crawlspace can create humidity/mold problems. I'd install a humidity monitor.

  2. Expert Member
    Akos | | #2

    Rodents need to be dealt with first as they will happily live in SPF.

    You dont want a vapor barrier between it and the rest of your house so no bubble wrap. Plus it is at best R3, not worth the hassle.

    The best bet is a thin layer of mineral wool, you dont want too much R value othwise the crawl space would get too cold and cause mold issues. I would install something like safe and sound. At R10 is about right.

    You can also crank up the temp in your loop till tue floor feels warm enough. Since the crawlspace is part of your conditioned space, extra heat there is not lost.

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