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Community and Q&A

Is this an airtight duct?

Steve Knapp CZ 3A Georgia | Posted in Green Building Techniques on

I have a supply and exhaust line roughed in for an upstairs ERV. These lines are running in an unvented attic space.

So the contractor taped the joints but not the seams. Do you need to tape and/or mastic the seams to properly seal these types of lines?

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  1. GBA Editor
    Martin Holladay | | #1

    There is no reason (from an energy perspective) to be particularly worried about the airtightness of the fresh air duct or exhaust duct of an ERV. The ducts look fine.

    If the ducts were located in the conditioned space of your home, or if they were conveying conditioned air from a furnace or air conditioner, it might be worth sealing the long seams parallel to the length of the galvanized ductwork. But for this type of ventilation ductwork, I don't think it matters.

  2. Steve Knapp CZ 3A Georgia | | #2

    Hi Martin.

    Thanks. That answers my question. Since the attic will be a sealed and conditioned space, I will have the contractor seal the long seam or replace the run with insulated flex duct.

  3. Expert Member
    Dana Dorsett | | #3

    Keep the hard-piping, and don't sweat the sealing as long as it's entirely within the thermal and pressure boundary of the house. You say the attic is sealed and conditioned, in which case there is not point to replacing it with insulated duct.

    Flex ducts are generally crummy stuff IMHO, with lots more ways to mis-install them, and with higher air-handler resistance to boot. I'd be loathe to replace hard-ducts with flex without some pretty compelling reasons. YMMV.

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