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Thread: How far off

  1. #1
    Join Date
    Dec 2002
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    143

    How far off

    I thought I had read somewhere on the boards that ductwork should never be directly butted against underside of the floor joists raher recessed slightly as to not transmit sound...This is the main trunk line in which the 6'' round branches off to various rooms... A section of the main run seems to be butted directly to the joist and would like to recess before the drywall goes up.. Would this be advisable.....one area of the run always seems to make popping/creaking noises after the heat goes off...could it be to tight in this area...anything to do to alleviate this?

  2. #2
    Join Date
    Jul 2008
    Location
    Alabama
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    658
    call the guy that installed the system, he will be able to help with the noise.

    i see trunks directly on the floor system and have had no problems with noise.
    You're only as good as your customer will allow you to be.........If they want junk, sell them junk, but make your junk look neat!!!

  3. #3
    Join Date
    Dec 2003
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    709
    1" below joists is standard although I dont know where it is in the code, I dont believe it is a mechanical code, maybe a building code.

    Also, this may not alleviate the popping because the duct will still not be flexible. Sometimes with popping it is because the duct wasnt cross-broke and it is floppy, a long l-bracket can be screw to the bottom of the duct to stiffen it up, or often I seem sheet metal in the shape of a v with 1/2" flanges at both sides to screw across the bottom of the duct.
    A flexible connector at some point too could be helpful, this will put a break in the connection between the furnace and the ductwork.

    Also, on returns it is very common to see the duct right up against the joists as to connect with joist pannings and make an airtight seal.

  4. #4
    Join Date
    Mar 2004
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    Quote Originally Posted by hivacer View Post
    1" below joists is standard although I dont know where it is in the code, I dont believe it is a mechanical code, maybe a building code.
    You see the 1" below the joist's just to make it easier to bend over the drive when a joint lines up with a joist.
    Karst means cave. So, I search for caves.

  5. #5
    Join Date
    Mar 2005
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    burlington county n.j.
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    for a gas furnace code requires 1" below joist for plenum and first 3' of trunk.

  6. #6
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    Jan 2009
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    Keokuk, IA
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    Quote Originally Posted by t527ed View Post
    for a gas furnace code requires 1" below joist for plenum and first 3' of trunk.
    Just curious, what's the reason for this other than possible noise? My ductwork butts up against the joists. I don't sem to have any vibrations or any issues I can tell related to it's mounting. Mounting it 1" lower would reduce head clearance in my basement, or require major duct modifications. Of course in my city, they don't do much for inspections. My home was boult in 1968.

  7. #7
    Join Date
    Dec 2007
    Location
    Cedar Grove, Wi-Sheboygan
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    1,582
    The noise is from expansion contraction from the hot air in the furnace, when the frunace first fires up the hot air expands the duct work, then a few minutes after the furnaces finishes it's call for heat the ducts cool and contract causeing noise again, This can be remedy by adding some small L brackets on a diagonal with on the top,bottom or both sides.

  8. #8
    Join Date
    Jul 2005
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    717
    Quote Originally Posted by t527ed View Post
    for a gas furnace code requires 1" below joist for plenum and first 3' of trunk.
    __________________________________________________ ___________
    This is good advice. Also, in some areas of the N. America,any heating duct should be at least 1" away from combustibles. Seems like good idea especially if a hi-limit switch was ever to fail.

    Note; it was mentioned earlier in a post by 'karsthuntr',that the main reason the duct is 1" away from the joist is so that a drive clip can be bent over......LOL ,... next joke ...pleeeeezzzz

  9. #9
    Join Date
    Mar 2005
    Location
    burlington county n.j.
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    Quote Originally Posted by motoguy128 View Post
    Just curious, what's the reason for this other than possible noise? My ductwork butts up against the joists. I don't sem to have any vibrations or any issues I can tell related to it's mounting. Mounting it 1" lower would reduce head clearance in my basement, or require major duct modifications. Of course in my city, they don't do much for inspections. My home was boult in 1968.
    1" is required as part of fire code in case of blower and limit failure.

  10. #10
    Join Date
    Feb 2007
    Location
    Great Lakes Region
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    575
    you mostly see duct attached directly to the floor joists to preserve the precious ceiling height of basements where every inch counts

  11. #11
    Join Date
    Feb 2007
    Posts
    999
    Quote Originally Posted by t527ed View Post
    for a gas furnace code requires 1" below joist for plenum and first 3' of trunk.
    How long has that been code in NJ?

    Amp

  12. #12
    Join Date
    Oct 2008
    Location
    Tol.,Oh.
    Posts
    80
    the 1" from the plenum & 4' from furnace is code here in N.W.Ohio. it's a fire code. ithink people leave it 1" down so they do'nt have to mess w/1" offset. the return duct is almost always tight against the joice.

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