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  1. #1
    Join Date
    Jun 2003
    Posts
    23

    Rafter through plenum?

    I had a new central AC system installed about a year and a half ago, and I am wondering if what they did is allowed. The plenum on top of the furnace/A-coil needed to be slightly larger to fit the size of the new system, so the installer enlarged the plenum by building it around one of the rafters that was directly above the furnace. So now the rafter goes right through the plenum. It seems to be sealed well around the rafter. I'm sure that this isn't recommended, but is this allowed by code, and will it cause any problems down the road? I don't think that I want the installer touching anything else at this point, so I will do any changes necessary, but if it will be "OK", while not good practice, I'll leave it alone.Thanks.

  2. #2
    Join Date
    Jan 2009
    Location
    Indiana
    Posts
    3,228
    sealed how? is the rafter exposed inside the plenum? Pictures would be worth a 1000 words.

  3. #3
    Join Date
    Jun 2003
    Posts
    23
    I'm pretty sure that the rafter is exposed inside the plenum, they used white duct sealant where the insulation board of the plenum meets the rafter. There is no air leaking from the joints. I would add a picture, but I don't know how to do that.

  4. #4
    Join Date
    Jun 2010
    Location
    Philadelphia PA
    Posts
    2,190
    Building cavities that I believe consist of building components like studs and joist are NOT allowed as duct for anything other than return air
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

  5. #5
    Join Date
    Oct 2010
    Location
    Houston, Tx
    Posts
    2,093
    Quote Originally Posted by johnkjr View Post
    I'm pretty sure that the rafter is exposed inside the plenum, they used white duct sealant where the insulation board of the plenum meets the rafter. There is no air leaking from the joints. I would add a picture, but I don't know how to do that.
    How far back in the plenum is this rafter and how far forward in relation to the rafter if at all are any duct take off's. Does your system seem to be performing correctly, are all vents throghout the home receiving air?

    To post pics, you can download them onto a pictrure hosting site such as photobucket and then in here and on a new reply, hit the little disk icon thing above the reply box and insert by way of cut 'n' paste the direct link from pic from photobucket into the address bar that will have popped up after clicking on the "insert image" icon and submit.

  6. #6
    Join Date
    Mar 2008
    Location
    Long Beach, CA
    Posts
    3,374
    Quote Originally Posted by genduct View Post
    Building cavities that I believe consist of building components like studs and joist are NOT allowed as duct for anything other than return air
    That is not my experience. In the City of Redondo Beach, CA the inspectors caught my HVAC installers using a small portion of a stud wall for a return path. They made them line that area with sheet metal. Id say raw framing within the return path is a no-no. Simply call your local building dept early in the morning before they hit the streets, they will gladly answer your question. When you get your answer please report back here.

  7. #7
    Join Date
    Dec 2010
    Location
    Down by the river
    Posts
    1,646
    It used to be common to just pan off a joist or rafter bay for return use, Supply is definatly a no-no. They have pretty much done away with raw wood return cavities now in my area.

  8. #8
    Join Date
    Jun 2003
    Posts
    23
    Here are some pictures of what I am talking about (I hope)
    Attached Images Attached Images   

  9. #9
    Join Date
    Jul 2009
    Location
    Plant City, Florida
    Posts
    2,198
    Quote Originally Posted by johnkjr View Post
    Here are some pictures of what I am talking about (I hope)
    That isn't a rafter, it is the botton chord of a truss.

    Hack work, but I guess since he sealed around it, that makes it good hack work,

    at least he didn't do what most a/c guys do and cut the truss.

  10. #10
    Join Date
    Jan 2002
    Posts
    1,196
    That's some funny stuff!

    If it's the supply plenum, bad. If it's the return plenum, only if they had no choice.

  11. #11
    Join Date
    Jan 2002
    Posts
    1,196
    Quote Originally Posted by bwalley View Post
    That isn't a rafter, it is the botton chord of a truss.

    Hack work, but I guess since he sealed around it, that makes it good hack work,

    at least he didn't do what most a/c guys do and cut the truss.
    "good hack work" LOL!

  12. #12
    Join Date
    Jun 2003
    Posts
    23
    [QUOTE=Roadhouse;8979771]How far back in the plenum is this rafter and how far forward in relation to the rafter if at all are any duct take off's. Does your system seem to be performing correctly, are all vents throghout the home receiving air?

    The system is performing just fine. All vents seem to be blowing at least as good, or better than the old system. I have attached a couple of pics in another post.

  13. #13
    Join Date
    Oct 2010
    Location
    Houston, Tx
    Posts
    2,093
    Judging by your pics, there doesn't seem to be a whole lot of room to work with and although not the prettiest of work it does look solid so I have to ask again, how is your system performing? Seemingly it would appear since it's been a year and a half, pretty decently and up to par.

    Can I ask where was and how was the old system placed? The return?

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