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Fiberglass vs. foam board insulation near a chimney

Post in 'DIY and General non-hearth advice' started by Chuck-OH, Jan 20, 2009.

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  1. Chuck-OH

    Chuck-OH New Member

    Joined:
    Dec 24, 2008
    Messages:
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    Loc:
    Ohio
    I'm replacing an old paneled wall that surrounds the original masonry fireplace. Took down the paneling, found 1950's fiberglass batts falling apart behind the paneling, and removed it all. Now need to re-insulate before drywalling.

    I'd rather use polyurethane foam board, but am wondering if can be placed above the hearth area. The bays are made of 2x4 stud sides, and at the back, are made of some type of hardboard (not plywood), and behind that must be the masonry wall of the chimney. The chimney is an exterior one, and I'm assuming since the hardboard was placed there originally, that area does not get hot. Would it then make sense that polyurethane is okay to go in there?

    The old paneling had been there 60 years, and did not look discolored above the hearth, though I don't know how often wood was burned in the fireplace. At present, there's a gas insert there, with a stainless steel liner, so the heat is much less. I'm just worried that if someday someone converted it back to wood, and fired it up, would the polyurethane melt/smell etc.

    Does this sound right to anyone?

    Thanks.

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  2. Dune

    Dune Minister of Fire

    Joined:
    Jan 14, 2008
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    Definitely agree with above, fiberglass is hard to ignite, foam burns with poisonous fumes.
  3. coolidge

    coolidge Member

    Joined:
    Dec 16, 2008
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    181
    Loc:
    Maine
    You could also use a mineral wool insulation. It is rated for 2150 degrees. Not shure what the price diff. is between fiberglass and the wool but just an idea.
  4. oconnor

    oconnor Minister of Fire

    Joined:
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    Messages:
    1,062
    Loc:
    Nova Scotia
    Chimney needs an airspace around it - latest codes ask for 2 inches for solid fuels.

    Don't fill the space at all is my recommendation.
  5. DAKSY

    DAKSY Patriot Guard Rider Staff Member

    Joined:
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    5,312
    Loc:
    Averill Park, NY, on Burden Lake II...
    Add one vote to the above...DO NOT put anything into that air space...
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