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  • Joist Cavity Return Air Question

    HVAC installer made it so 2 of my joist cavaties are return air "ducts". Both are about 12"x15"x15' long between the TJI's. Question - before the sheetrock goes on would you line the bare wood with anything or paint some kinda coating on the wood? Seems like bare OSB will hold dust very well and what if some of the knockouts fall out creating holes to suck fiberglass into system? What about noise concern?
    Would you worry about it or S. Rock & Forget? Thanks.

  • #2
    Re: Joist Cavity Return Air Question

    i don't do residential but i would not want this in my house

    it will collect a lot of dust and if they just screw the rock to the joist then you will be sucking air from above all the rock because it does not seal to the joist.
    this will take away return air from the upstairs .if the down stairs is not AC then you take a chance of it sweeting then comes the mold

    i would rather see a return duct all the way back to the air handler

    this is my 2 cents
    Charlie

    My seek the peek fundraiser page
    http://observatory.mountwashington.o...nal&fr_id=1040


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    • #3
      Re: Joist Cavity Return Air Question

      This is illegal in almost all areas and extremely unsafe as it can spread fires. He needs to run duct for your return.
      Buy cheap, buy twice.

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      • #4
        Re: Joist Cavity Return Air Question

        That's how its done up here, been that way for years too. It's common practice to use joist spaces and stud spaces as return ducts. Although its not the best, most codes allow this method. Some info here http://resourcecenter.pnl.gov/cocoon...r/article//130
        Last edited by Hondahead; 12-23-2007, 11:33 PM.
        You will never expand your mind, if you do not challenge your beliefs.

        By the reading of this post, you acknowledge and agree that the poster shall not be responsible or liable, directly or indirectly, for any damage or loss caused or alleged to be caused by or in connection with use of or reliance on any content contained herein.

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        • #5
          Re: Joist Cavity Return Air Question

          Originally posted by Hondahead View Post
          That's how its done up here, been that way for years too. It's common practice to use joist spaces and stud spaces as return ducts. Although its not the best, most codes allow this method. Some info here http://resourcecenter.pnl.gov/cocoon...r/article//130
          Different strokes for different folks but is a good reminder that nothing is set in stone. Check your local codes.
          Buy cheap, buy twice.

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          • #6
            Re: Joist Cavity Return Air Question

            Originally posted by Hondahead View Post
            That's how its done up here, been that way for years too. It's common practice to use joist spaces and stud spaces as return ducts. Although its not the best, most codes allow this method. Some info here http://resourcecenter.pnl.gov/cocoon...r/article//130
            good info and i still would not want it in my house so i would not do it in anyone else's house or building
            Charlie

            My seek the peek fundraiser page
            http://observatory.mountwashington.o...nal&fr_id=1040


            http://www.mountwashington.org/weather/conditions.php

            new work pictures 12/09
            http://public.fotki.com/hvachawk/

            Comment


            • #7
              Re: Joist Cavity Return Air Question

              Originally posted by 'Stormin View Post
              HVAC installer made it so 2 of my joist cavaties are return air "ducts". Both are about 12"x15"x15' long between the TJI's. Question - before the sheetrock goes on would you line the bare wood with anything or paint some kinda coating on the wood? Seems like bare OSB will hold dust very well and what if some of the knockouts fall out creating holes to suck fiberglass into system? What about noise concern?
              Would you worry about it or S. Rock & Forget? Thanks.
              This installation is the norm and legal for residential construction under both the UMC and the IMC. You live in an area where they use the IMC so it is legal. As far as noise it will be quieter than it would be if it were a sheet metal duct but not as quite as an insulated duct.

              I believe the restrictions on having gyp in the ducts are it can not be used for evaporative coolers, fire resistive construction between two dwelling units or ducts which convey air which is colder than 50 degrees Fahrenheit or hotter than 125 degrees Fahrenheit.

              Mark
              "Somewhere a Village is Missing Twelve Idiots!" - Casey Anthony

              I never lost a cent on the jobs I didn't get!

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              • #8
                Re: Joist Cavity Return Air Question

                Joist panning has been in use here for about 80 or so years. Every new house I do has joist panning. My houses range from the everyday $200k single furnace, to multi-million dollar homes with several systems. They all have joist panning. This style of return duct has proven itself to be more efficient than round piping each individual return. As for the dust thats going to collect in the return, if you understand anything about airflow dynamics you know theres a boundry layer that exists between the wall of the duct and the airflow 'wedge' in which theres little to no airflow present. Dust is going to collect no matter what the construction is.

                UMC 03 Chapter 6
                602.2 Combustibles within ducts or plenums
                Materials within ducts or plenums shall have a flame-spread index of not more than 25 and a smoke-developed rating index of not more than 50 when tested as a composite product in accordance with ASTM E84 or ANSI/UL 723, Standard for Surface Burning Characteristics of Building Materials, or as a composite product in accordance with NFPA 255 Standard Method of Test of Surface Burning Characteristics of Building Materials, ASTM E 84-2001 of ANSI/UL, 723-96:

                Exceptions:
                (1) Return-air and outside-air ducts, plenums or concealed spaces that serve a dwelling unit shall be permitted to be of combustible construction.

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                • #9
                  Re: Joist Cavity Return Air Question

                  Learned something new today but I'm still not comfortable with it.
                  Buy cheap, buy twice.

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                  • #10
                    Re: Joist Cavity Return Air Question

                    Joist panning has been around for a very long time. It is acceptable in the national mechanical code and the international mech. code. There is no need for painting, or further lining of the space. Wires should not be installed in the cavity nor should plumbing or gas piping obviously.
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