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Thread: Joint Seals

  1. #1
    Join Date
    Mar 2008
    Posts
    4

    Joint Seals

    I recently had my a/c system completely replaced by a reputable dealer, including all ductwork. They did a great job except for one thing: they did not tape the bottom of the joints where the 4-foot sections of plenum join. The other 3 sides are sealed with mastic tape. The Unit sits on the roof trusses which is probably why the bottom was not taped.

    How much leakage can I expect by not having the fourth side of each joint taped? Should I try to get them to fix this?

    Also, the plenum is insulated with one inch duct insulation on the inside of the sheet metal (dealer says it has a value of R-4). I was looking at maybe adding 2" foil backed polystyrene rigid board to the outside of the plenum with glue and/or plastic straps. This would give me an additional R-8 of insulation. Would this be feasible or worthwhile?

  2. #2
    Join Date
    Apr 2001
    Location
    Camel City, NC
    Posts
    6,232
    Ask them to tape the joints. The current 2008 code requires R-8 for ducts in attics unless the attic space is inside the envelope of the structure.
    Be safe not fast. body parts don't grow back

  3. #3
    Join Date
    Jun 2001
    Location
    Louisville, KY
    Posts
    12,000
    Quote Originally Posted by selfemployed View Post
    Ask them to tape the joints. The current 2008 code requires R-8 for ducts in attics unless the attic space is inside the envelope of the structure.
    Careful on quoting code...

    Not all states have the same requirements.

    My great hack state is still R-6.
    Perhaps you should have read the instructions before calling.

  4. #4
    Join Date
    Apr 2001
    Location
    Camel City, NC
    Posts
    6,232

    Thanks Jr.

    I had put - May depend on where you live, but edited it out.
    Be safe not fast. body parts don't grow back

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