Hvac Rectangular Stack Inside Wall

Discussion in 'HVAC' started by tk3000, Dec 31, 2016.

  1. Dec 31, 2016 #1

    tk3000

    tk3000

    tk3000

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    Hello Folks,

    Recently, I started fixing and assembling ductwork inside the wall for the hvac. Some of the ductwork was simply missing, so I had to assemble entire rectangular ductwork out of 3.25"x10"x3ft half sections rectangular stack duct, s cleats, drive cleats, rectangular head (where the end forced vented grill will be present), stack boot (connecting the upper end of the stack to the ductwork in the attic). I also acquire the proper tools: bending/folding tools, snippets, etc.

    The following pics depicts the assembling stages:

    [​IMG]
    (part of the rectangular stack connected to the stack head, stack head has a flange that could be used to screw it to the bottom plate of the wall)

    [​IMG]


    [​IMG]

    [​IMG]
    (with connections made out of cleats and s-cleats, it is not a rigid structure, and was wondering if that is the way it is supposed to be?)

    So, I was wondering if that is the right approach to fabricate these ductwork stacks. Should be cleat connections be taped with foil tape? Should the whole stack be wrapped in reflectix insulation?

    thks!
     
    Last edited: Dec 31, 2016
  2. Dec 31, 2016 #2

    tk3000

    tk3000

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    Cont... (could only post so many images in one thread post)

    [​IMG]
    (dry fitting on spot inside walls)

    Last but not least, this is not a very rigid structure (the fabricate stack) to be rigidly erected inside the wall, and besides the flap present on the stack head at the bottom (which will be screwed to the bottom plate of the wall) there is nothing else supporting it; so, I was wondering what type of extra support -- if any -- should/could be added?

    Also, whereon the upper boot connect to the ductwork in the attic above it seems that it just fits in there... should tape be added to better seal it (can not use sheet metal screws, not enough clearance)
     
    Last edited: Dec 31, 2016
  3. Dec 31, 2016 #3

    Jeffh

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    YOu can add self-tapping sheet metal screws to the s-cleats about 2" in from either end, keep in mind you are going through about 5 layers of tin. This will give the wall stack duct some added rigidity as short drive cleats dont stiffen it up much. Wouldnt hurt to add foil tape to the joints.
    You can add strappings(or a long 16" drive cleat) across each stud on other side, and screw it to the ductwork as well. That will secure it a bit better in place.
    Round connections should be fastened with at least 3 screws, but at least one would be nice. Taping it wont hurt afterwards.

    Trim your drives down to a 1" fold over, you got like 2-3", makes it look shoddy.
     
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  4. Dec 31, 2016 #4

    beachguy005

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    If that's a return air duct, they usually just use the studs and wallboard on both sides as the air plenum, and not actual duct work. If you are going to use it, when you attach it to the bottom you should raise it up high enough for baseboard trim to go under the grill.
     
  5. Dec 31, 2016 #5

    buffalo

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    I think they sell a heavy guage strap that you would nail to the studs and then screw through into the duct to stiffen it . Is this a single story with duct in the attic ? I just used ceiling grills if that's the only reason your opening up the walls .

    And the previous poster is right , looks a bit low . Figure your grill is going to have a 1" flange on it , what's the height of the baseboard?
     
  6. Jan 1, 2017 #6

    tk3000

    tk3000

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    No, this is not an air duct return (I realize that they don't need an actual duct for returns). It is a force air duct.

    By raising the stack at the bottom you mean maybe adding a piece of 2x4 to that segment of the bottom sill?

    thks
     
  7. Jan 1, 2017 #7

    tk3000

    tk3000

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    I will look into the heavy gauge straps, maybe once it screwed in place it will bee rigid enough.

    No, that is not only reason: the drywall was damaged so I would have to replace part of it anyways, besides I am also doing some electrical work along the way (albeit at a very slow pace lately)

    The previous stack (or what was remaining of it) had it head stack attached directly and square onto the bottom sill plate, that why I was planning to attach it directly there. Would a piece of 2x4 atop of the sill plate be enough to raise the stack?

    thks
     
  8. Jan 2, 2017 #8

    buffalo

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    As far as height , what's the floor going to be ? Carpet / hardwood ect , and how deep will it be ? Figure your grill on the wall will be an inch lower than the square opening . How tall is your trim ? If it's to low you may be into the baseboard trim is all.

    I tried searching the Web quick and couldn't locate the straps . Basically it's a 1" strip of metal , just a heavy guage like 18guage.

    I personally like oval wall stack , easier than slip and drive .
     
  9. Jan 2, 2017 #9

    nealtw

    nealtw

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    Ovals are nice but every time I have had to work on them, I have had to get the boot made, nobody has a pattern for it..
     
  10. Jan 2, 2017 #10

    nealtw

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    Fill the space between the studs and the boot at the bottom , screw the boot to it and you will have something to screw the grill to.

    Just a flat piece of sheet metal long enough to reach both studs screw in place,

    I like to lift them so the floor molding goes below.
     
  11. Jan 2, 2017 #11

    Jeffh

    Jeffh

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    Yes, a 2x4 near the bottem plate would work to raise the duct up. Id say about 4-6" to top of new 2x4 from finished floor height.
     
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  12. Jan 2, 2017 #12

    tk3000

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    I am planning on installing ceramic tiles in the new future, and since it is a slab there would be no backerboard. Baseboard: I don't know exactly but it should be basic type on the short size/side of the spectrum.

    I am also planning on wrapping the rectangular stack with reflectix type insulation. I saw some old one wrapped in a white (probably asbestos) type of thing.
     
  13. Jan 2, 2017 #13

    tk3000

    tk3000

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    By boot you mean the stack head where the register/grill will be attached to? How about the boot that connects to the ductwork above in the attic? I may not have enough room to screw it up there..

    :thbup:
     
  14. Jan 2, 2017 #14

    nealtw

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    tk3000 likes this.
  15. Jan 3, 2017 #15

    buffalo

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  16. Jan 3, 2017 #16

    buffalo

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    HMM , tile up the wall? This is where I look to the pros of other trades . But to keep it simple , if the grill is not going to hit anything , your good .:rofl:
     
  17. Jan 3, 2017 #17

    nealtw

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    It is a joke here, HVAC guys run the oval pipe down the wall and the stack head they install is a 6 x 6 x 10 box for the vent. Just had to find one a few months ago, had to send the sheet metal guy a drawing of what I wanted.
    It is easier to run the rectangle down the wall with a flat cap on the bottom and just cut a hole for the grill.
     
  18. Jan 3, 2017 #18

    buffalo

    buffalo

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    In that case your right , 10x easier . But then you need to duct it through the wall to the grill or else it blows into the wall . Not sure if that would cause a problem blowing any air into the wall cavity?
     
  19. Jan 3, 2017 #19

    nealtw

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    Nope fits tight to drywall, wrap the joint between dry wall and metal with tape.
    Cover with grill. I do cap the bottom of the 10x.
     
  20. Jan 3, 2017 #20

    tk3000

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    The difficult part in this case it removed the old flooring and its remanants (adhesives, black mastic, etc) in order to have a proper substrate for the thinset to adhere to. But the tiles are not going up to the wall

    As far as baseboard, on a second thought it seems that instead of accounting for its height of baseboard to simply eliminate the baseboard from under the grill. But I wlll make sure to pay attention to the clearance needed for the grill in any case, better be safe than sorry...
     
    Last edited: Jan 3, 2017

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