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Community and Q&A

Mastic and/or duct tape

chrisjohnston2112 | Posted in Energy Efficiency and Durability on

My house is currently under construction. The HVAC contractor has run flexible ductwork in conditioned and unconditioned spaces. He has attached it to the sheet metal floor vents with duct tape. Should I put mastic over the duct tape, or remove the tape, install a hose clamp, and mastic over that?

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  1. Riversong | | #1

    If it's the corrugated flexible ducting, you should replace it with smooth ducting , whether flexible or rigid, and make sure it's supported in straight runs (no sags). Otherwise the flow is dramatically reduced by the static friction and turbulence. Also, any ductwork in an unconditioned space must be both sealed and insulated. Ordinary duct tape is not approved for this use. I would remove it and replace it with either duct mastic or butyl-foil duct tape. There should also be mechanical connectors, either screws or clamps. Tape and mastic is for sealing, not for mechanical attachment.

  2. GBA Editor
    Martin Holladay | | #2

    It's impossible to tell from your question whether your HVAC contractor has done it right. There are some good duct tapes out there; however, run-of-the-mill hardware store duct tape should not be used.

    In an unconditioned space, all ducts must be insulated.

    For more information, check out:
    Sealing Ducts

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