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spray foam directly on radiant plates?

Royboy Member Posts: 221
I have a client for whom I am doing a radiant floor with heat transfer plates under the subfloor. this floor will be over unheated space and he plans to spray foam it along with the rest of the envelope. I know the recommended procedure is to keep insulation away from the transfer plates & maintain a dead air space around them. and ... can anyone comment on whether spraying foam directly over the tube/plates just absolutely shouldn't be done - or whether its more of a less-optimal strategy that can be done but doesn't perform as well? my sense is that by foaming you would not have that hot air cavity that would tend to indirectly warm all the subfloor that doesn't have contact with the plates. is that the primary concern or are there other things I'm not thinking of?

not having to create that dead air space would obviously be quite a bit easier ...


  • Paul Pollets
    Paul Pollets Member Posts: 3,509
    Foam on plates

    While the dead air space is not needed, it is not the best idea to get the foam on the piping and plates. There may be a chemical reaction which could affect the piping. Batts are best. It's also impossible to access the piping once it's foamed.
  • hot_rod
    hot_rod Member Posts: 16,327
    one caution

    I had 3 or 4 of my jobs foamed over the years, going on 8 years or more now. I did contact the tube manufacturer before we sprayed.

    That foam will find the smallest of gaps including any areas where the plate is not in perfect contact with the floor.

    And finding a leak from a flooring nail can be a big hassle and mess, I can tell you :)

    I sure like the way foam seals the end, band joist area. That is a common infiltration leak area where the framing contacts the foundation, etc.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Zman
    Zman Member Posts: 7,330
    Don't do it...

    Aside from the potential for a chemical reaction. If the insulators spray in too big a lift, the heat can melt the pex. This has happened and it really stinks. We just did one where we used 1/2" foil faced polyiso to separate the foam from the plates.We just cut it with a utility knife and used foil tape to secure and seal it to the joists. It worked like a charm

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • SWEI
    SWEI Member Posts: 7,356
    Wet spray cellulose on plates

    works like a charm.
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