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Seal Flex Duct Connections With Fire Block Spray Foam?

AtticAdventures | Posted in Energy Efficiency and Durability on

Is it acceptable to seal flex duct connections (at supply plenum, ceiling boot, where main supply lines branch into multiple lines) using a can of fire blocking spray foam? Thank You.

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  1. GBA Editor
    Martin Holladay | | #1

    It's acceptable, but canned spray foam may not provide a dependable and durable air seal. Either high-quality foil HVAC tape or mastic is usually a better choice for air sealing duct seams.

    If you do end up using spray foam, a thicker layer will provide a better air seal than a thin layer.

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