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Community and Q&A

Interior wall stud bay as HVAC cold air return

user-2994765 | Posted in Mechanicals on

What are best practices for sealing interior stud bays as HVAC cold air returns? Common practice is to use studs and drywall. Am in midst of new build in climate zone 4 in Louisville, KY. Am keeping all ducts and returns in conditioned space.

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  1. Expert Member
    Dana Dorsett | | #1

    Installing 3.25" x cross section hard duct designed to be accommodated by stud bays, seams & joints sealed with duct mastic works.

  2. GBA Editor
    Martin Holladay | | #2

    Although you may be describing "common practice" in your area, building experts have advised against the use of stud bays as ducts for at least the last 30 years. The practice is outlawed by some building codes, and is forbidden by most green building programs.

    If you have to run a duct in a stud bay, you should purchase the type of galvanized ductwork described by Dana. The technical name for this type of duct is "wallstack," and it commonly measures 3 1/4" x 14" or 3 1/4" x 22".

    All of that said, wallstack is mostly useless, because a properly designed return air system will almost always require much larger ducts than 3 1/4" x 14".

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