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Community and Q&A

OK to foam forced air duct?

David Fay | Posted in Green Building Techniques on

I have forced air ducts in an unheated basement that (a) leak, (b) have no modern insulation, and (c) are covered with asbestos. It occurred to me that spray foam might be a good solution to all three problems. Does this make sense? Will heat degrade the foam? Closed cell or open? Gotchas?

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  1. GBA Editor
    Martin Holladay | | #1

    1. There's no real reason you can't cover ducts with closed-cell spray foam. HOWEVER,

    2. It's not worth investing in an expensive layer of spray foam if the existing ductwork is in very bad shape.

    Ideally, you want the ducts to be solid and well-supported with hangers or strapping. If the ducts are unsound and poorly supported, it might be best -- and it might even be cheaper -- to replace the ductwork.

  2. David Fay | | #2


    Thanks for the advice. I didn't mean to imply that the ducts were in very bad shape. They are actually in fine shape and well supported. I don't see any reason to replace them, especially since doing so would require asbestos remediation. I was just wondering whether with spray foam I could kill three birds with one stone.

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