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Community and Q&A

Ventilation ducts in exterior walls

user-1137156 | Posted in Energy Efficiency and Durability on

I’ll need some form of duct to get fresh outside air to my ERV and another to dump the exhaust..
I’m building with double stud walls insulated to r40 whole wall. The ERV will be in the basement. I have a place where I can in effect move the walls inward so the duct will be outside the insulation as it crosses the sub floor. Is there any reason to use insulated duct? Would a rectangular duct made of fiberglass “duct board” work? Any reason to not use galvanized steel ‘sheet metal’ duct sections?

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  1. GBA Editor
    Martin Holladay | | #1

    I assume you meant to write that the ducts will be "inside the insulation," not "outside the insulation."

    You didn't mention your climate. But in a cold climate, the duct that conveys fresh outdoor air to your ERV will be quite cold in winter. If you use uninsulated galvanized ductwork, you are setting up a situation that encourages condensation. That's why you should use insulated ductwork.

  2. user-1137156 | | #2

    No I meant exactly what I said. Above the sub floor these ducts will be outside the insulation. the insulated wall is made much thicker for a short distance to accommodate the ducts and to place the insulation (r45) on the interior side of the ducts, only the fiberboard sheathing and thin brick is between them and the great outdoors.

  3. GBA Editor
    Martin Holladay | | #3

    Ducts in the location that you describe will still be cold. The only question is whether the air in this closed chase will contain enough moisture to cause a condensation problem. To my mind, skipping the duct insulation is a silly risk. It's far better to spend $10 on duct insulation than to risk condensation, drips, and rot.

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