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Thread: Insulate plenum?

  1. #1

    Default Insulate plenum?

    Should you always insulate the plenum on an attic furnace/ac (horizontal)setup? The plenum is about 7 feet long x ~2 feet wide x ~1 foot high. 6 - 8" insulated fleixible duct lines come off of the plenum.

    Mine is an 80% furnace, 92% AC.
    Last edited by bmwpower; May 12th, 2005 at 11:40 PM.

  2. #2

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    Quote Originally Posted by bmwpower
    Should you always insulate the plenum on an attic furnace...
    There is no IRC mandate to do so, but the IECC does seem to have this requirement if that document is also in force in your area. If you do insulate the plenum, the IRC does require you to use a vapor barrier on the exterior of the insulation or use duct insulation blankets with integral vapor barrier and tape the seam(s). Duct insulation may not pass through a fire wall or fire rated floor/ceiling. The ductwork passes through the fire rated assembly without insulation, and then you insulate the exposed ductwork on both sides. I just thought I'd add that in case that applied to your garage. If your plenum is made out of ductboard, then it's already insulated so to speak.
    "Nothing is foolproof to a sufficiently talented fool"

  3. #3

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    Do you feel insulation would be necessary in this case? If I don't need to do it, I probably won't unless it saves a good amount of energy.

  4. #4

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    If it is sheet metal, personally I would as a matter of good practice. I'm not sure how much energy savings may be realized, though.
    "Nothing is foolproof to a sufficiently talented fool"

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