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Installing radiant under existing Hardwood floors with questionable underlayment

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knownspace
knownspace Member Posts: 2
in Radiant Heating
I am concerned about the underlayment in my older hardwood floors and how it will react to radiant heat that I plan to install. The paper has a thin layer of asphalt sandwiched in between. I know this product is still used today under hardwood floors but I am worried that there may be some outgassing of the asphalt layer when the floors are heated. I plan on plates underneath and a water temp of 110 max. I am hoping someone has experience with this and can share their knowledge. Thank you.

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  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    edited August 2020
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    I used roof underlayment (black paper), under my tubing/wet bed/ceramic tile. Never had any smell or out gassing.
    Rosin paper is used under hardwood. Never seen anything but that, unless it’s something with asbestos in it.

    There was an error rendering this rich post.

  • hot_rod
    hot_rod Member Posts: 22,158
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    Seems like you need to be above 120 - 130m before asphalt impregnated felt paper starts to off gas.

    I have seen outgassing in high SWT temperature rubber tube staple up where 160F was required to meet loads.
    Outdoor reset keeps temperatures to a minimun and avoids wide swings.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • kenjohnson
    kenjohnson Member Posts: 85
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    I was worried about this also with an installation under hardwood floors in a 1926 house renovation. I've run up to 127 degrees F in a test situation and had no odor whatsoever. I'm not sure what exact material the underlayment is, but it was probably used universally in houses of that era.

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