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Thread: In-WALL air return?

  1. #1

    Default In-WALL air return?

    I asked this elsewhere, no reply yet... What do you guys think?

    When our furnace was replaced, the installers put some new ducting in, including this 2nd floor air return duct. Each floor has separate ducting and itís own furnace.

    Because this duct butts right against the door trim and goes almost all the way to the wall on the right, itís hard to finish it with drywall.

    I am thinking of removing this return duct altogether, framing the area with 2x2ís and finishing with drywall. This way, the air return will be built inside a wall cavity and will actually have a slightly greater cross section area.

    Do you see any problem with doing it this way?

    Any suggestions on how to finish the inside walls of this new ďductĒ? Should I paint it with glossy paint for smoother airflow or should I use any other special paint/finish?

    Thanks


  2. #2
    Network Engineer rmelo99's Avatar
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    I've seen return trunks/runs created by panning sections of floor joists instead of using ducting, sort of what you are talking about doing.

    I think that isn't an approved way to do it everywhere or as wide spread as it used to be. In addition if you are going between floors, you have fire code concerns to deal with. Usually openings between floors must be sealed and/or blocked to prevent the speed of fire spreading. I would check with your building inspector before doing that.

    From a technical point of view, yes it should work because you are essentially creating a duct using a wall cavity.

    In my house we had a similar issue, with ducts and ceiling height.How bout just putting a 2x on the left to screw sheetrock into and glue the rest onto the duct. We're talking 1/2" here and u can do 3/8" if u needed to. Just my .02

  3. #3

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    Quote Originally Posted by rmelo99 View Post
    I've seen return trunks/runs created by panning sections of floor joists instead of using ducting, sort of what you are talking about doing.

    I think that isn't an approved way to do it everywhere or as wide spread as it used to be. In addition if you are going between floors, you have fire code concerns to deal with. Usually openings between floors must be sealed and/or blocked to prevent the speed of fire spreading. I would check with your building inspector before doing that.

    From a technical point of view, yes it should work because you are essentially creating a duct using a wall cavity.

    In my house we had a similar issue, with ducts and ceiling height.How bout just putting a 2x on the left to screw sheetrock into and glue the rest onto the duct. We're talking 1/2" here and u can do 3/8" if u needed to. Just my .02
    I never thought of a fire code affecting this, since the stairs to the upstairs don't require a door. But instinctively was thinking of using the concrete sheet rock to line the inside and the finishing wall of the new return. I think that would address the speed of fire spreading problem.

    The reason I can't just glue the drywall to the face of the duct is because it gives almost an inch when pressed, so the wall would not be stable.

  4. #4
    DIY Senior Member burleymike's Avatar
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    They should have made the duct wider and less deep so you could frame up a wall. For fire proofing and air quality reasons I would not use the wall cavity as a duct, it used to be done like that though, talk to your inspector about it.

    The other problem with using the wall cavity is that if it is a 2x4 wall it will be much smaller than that duct reducing air flow. Assuming they calculated the duct size properly that will mess up your system. Especially if you have A/C you could end up with your evaporator icing.

  5. #5

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    Quote Originally Posted by burleymike View Post
    They should have made the duct wider and less deep so you could frame up a wall. For fire proofing and air quality reasons I would not use the wall cavity as a duct, it used to be done like that though, talk to your inspector about it.

    The other problem with using the wall cavity is that if it is a 2x4 wall it will be much smaller than that duct reducing air flow. Assuming they calculated the duct size properly that will mess up your system. Especially if you have A/C you could end up with your evaporator icing.
    Yes, they should've done a better job installing that duct. Unfortunately, I have to deal with what it is.
    Part of the reason I was asking about the best paint/finish was the "air quality" consideration.

    As far as the size of the wall cavity, it actually will be bigger than the current duct, since all I'm doing is putting a wall between the 2 doorways that you see, after removing the duct.

  6. #6
    DIY Senior Member burleymike's Avatar
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    What will work is to remove the existing duct and build a new wall like you want to do. Then line the new cavity with sheet metal and seal all the joints with mastic. You will save some money not having to have a shop make up a new duct.

  7. #7

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    Quote Originally Posted by burleymike View Post
    What will work is to remove the existing duct and build a new wall like you want to do. Then line the new cavity with sheet metal and seal all the joints with mastic. You will save some money not having to have a shop make up a new duct.
    That's an interesting idea, but I'd rather not deal with sheet metal.

    What other material can I use?

    I am thinking of that foil lined insulation with an adhesive on one side. Would something like that be an acceptable alternative? What different types are there?

  8. #8
    DIY Senior Member gardner's Avatar
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    Quote Originally Posted by tl2tl View Post
    rather not deal with sheet metal
    It's a duct. Get some snips and gloves and learn to like it.

    If you will enclose the space, I would also look into opening up the wall behind the duct. If you can move the duct back into the space you can gain room on the front side. Even just removing a couple of inches of plaster and lathe will give you that much more space to work with.

  9. #9

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    Quote Originally Posted by gardner View Post
    It's a duct. Get some snips and gloves and learn to like it.
    That's funny.

    Quote Originally Posted by gardner View Post
    If you will enclose the space, I would also look into opening up the wall behind the duct. If you can move the duct back into the space you can gain room on the front side. Even just removing a couple of inches of plaster and lathe will give you that much more space to work with.
    Can't touch the wall behind the duct as it already houses a supply duct within it.

    I appreciate all the suggestions from everyone so far and I'm open to more ideas.

  10. #10
    Network Engineer rmelo99's Avatar
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    If you dont want to deal with sheetmetal then you can use fiberboard duct material. One point to note is that because it is 1/2" or so thick, unlike metal ductwork that will cut into the inside dimensions of the duct run.

  11. #11

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    Quote Originally Posted by rmelo99 View Post
    If you dont want to deal with sheetmetal then you can use fiberboard duct material. One point to note is that because it is 1/2" or so thick, unlike metal ductwork that will cut into the inside dimensions of the duct run.
    Thanks, I was just reading about the duct board.
    That's one of the materials I am considering.

  12. #12
    Master Plumber nhmaster's Avatar
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    You can use joist bays for cold air return provided no wiring or other mechanicals are in the same cavity.

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