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  • rectangular ductwork

    I'm adding a room to the back of my house. It's going to allow me to install a return-air duct to a loft area in the existing house (reducing stratification). So I'll run a boxed-in drywall chase (is this the right word ?) up the wall of the addition that backs against the existing house, containing the duct from the crawlspace (where the air handler is) to the return-air box in the back wall of the loft.

    For reasons mainly of the shape I'd like for this "chase", I would rather use some fairly thin rectangular ductwork (maybe 6-8" by 16-20" or so) instead of 12" round flexduct. Searching for this product, it seems mainly to come in 4ft lengths, making me think it's not really meant for what I'm trying to do. Am I mistaken ?

    It also occurs to me that maybe I don't need ductwork at all - why not just let this drywalled-in chase BE the duct ? Caulking it well, of course. Any leakage is just going to suck air in from the new room, which is kinda what a return-air duct is supposed to do in the first place.

    Another issue ... I mainly want the loft return to reduce winter-time stratification - sucking all that hot air in the loft into the HVAC, to help keep the house warm and the loft from being too hot. However, in the summer-time, I'm happy to not use the loft. In which case the de-stratification just increases the cooling load. So would it make sense to shut off the new return-air duct in the summer, with some kind of valve ?

    Thanks.
    Last edited by RustyShackleford; 08-13-2012, 08:33 PM.

  • #2
    Re: rectangular ductwork

    Actually doing a little research, looks like I can just frame the chase and line it with one of the products here:

    http://www.johnstonesupply.com/store...opularity-desc

    Looks like the QuietR Fiberglass Ductboard might be just the ticket. I talked to bldg inspectors and it seems ok with them (they do not require metal lining).
    Last edited by RustyShackleford; 08-23-2012, 02:49 PM.

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    • #3
      Re: rectangular ductwork

      For a return air, you don't need any of that stuff--just box it in. It is done all the time.

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      • #4
        Re: rectangular ductwork

        Originally posted by Pipestone Kid View Post
        For a return air, you don't need any of that stuff--just box it in. It is done all the time.
        Thanks for replying ... Yeah I guess it doesn't matter if it's insulated or even airtight, since it's in the conditioned living space. No worry about sheetrock dust, sawdust, etc getting sucked into the air handler ?

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        • #5
          Re: rectangular ductwork

          I personally do not like duct board. If you can/want to do it with sheet metal the 4' sections go together with things called drives and locks. It could also be prefabbed by a sheet metal shop. They make dampers that go in duct work to adjust airflow. If you box it in with only sheetrock, get a filter in there before it goes into the air handler to catch the debris for a bit then take it out and seal it up. If it will not be going through a filter at all make sure it does when you are done.
          AllurePlumbing.com
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          • #6
            Re: rectangular ductwork

            Thanks for you thoughts on this; I will let my HVAC man (not a pro, but knows what he's doing) decide how to go. Mainly, I wanted to make sure SOMETHING would work if I only allowed for a cross-section that's rectangular and thin.
            Originally posted by Gettinit View Post
            If it will not be going through a filter at all make sure it does when you are done.
            Sorry, I'm not sure what you mean by this sentence ...

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            • #7
              Re: rectangular ductwork

              Sorry, I'm not sure what you mean by this sentence ...

              Do not bypass your whole house filter with your new return.
              AllurePlumbing.com
              • leak detection
              • drain cleaning
              • utility locating
              • conductor fault locating
              • and other specialties.

              Greensboro NC, Winston-Salem NC, High Point NC, Thomasville NC, Kernersville NC

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