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  1. #1
    Join Date
    Sep 2012

    Default Insulating Attic Duct

    I live in OK in a 33 year old home. My return ducts are located in the attic and have a 1 inch fiberglass insulation blanket around it. The blankets exterior is white plastic. The return duct box has no insulation around it at all, only the tube part is insulated. Is this adequate or should I add another blanket to the tube part as well as the return duct box. If so, what type do you recommend and how thick? Installation techiques are appreciated!

  2. #2
    Join Date
    Jul 2010

    Default Re: Insulating Attic Duct

    Go to air condition suppliers (they are usually wholesale outlets), they have the right type of insulation you need.

  3. #3
    Join Date
    Dec 2007

    Default Re: Insulating Attic Duct

    To be clear here, the return duct is the one with the air filter in it. Where is you HVAC unit located, in the attic, in a closet or out side (all in one)? Now the ducts that distribute the conditioned air, there is a central, square duct called a trunk pr plenum, the individual ducts, usually round come off that. It sounds like you are using flex ducts for this, which has some insulation sandwiched between two layers of plastic/foil and supported by a spiral wire.

    The trunk/plenum may be insulated on the inside. The flex duct is now available with 2" fiberglass insulation instead of just 1 inch. You can buy insulation to go around the flex duct but I think it is less expensive to just replace the 1" fiberglass insulated flex ducts with 2" insulated flex ducts.

    To add insulation to the trunk/plenum, first seal all the seams, then use 2" foam boards with a foam board adhesive.

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