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Can unfaced polyiso be used for radiant heat systems?

JohnnyO46 | Posted in Energy Efficiency and Durability on

I have radiant tubing installed between floor joists. I’ve placed a foil reflective sheet beneath the tubing and though faced fiberglass insulation is recommended to be placed beneath the foil sheet, I want to use un-faced polyiso boards 3″ thick instead. The boards will be exposed to a heated, block wall, basement that is reasonably dry.
I would appreciate your comments.
Regards, JTO

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  1. Expert Member
    Dana Dorsett | | #1

    It's fine to use polyiso under the radiat floor, but note that the shorter 3" path through the wood has half the R-value as the 6" path you would have with R19 fiberglass. Either would be sufficient for zone isolation between the first floor & basement though (even R11 batts are "good enough".)

    If the tubing is tight to the subfloor or in aluminum heat spreaders there's almost zero benefit to the foil though.

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