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  1. #1
    Join Date
    Feb 2010
    Location
    Ontario Canada
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    1,341

    Duct in Attic insulation.

    I am about to install my first Attic air handler and duct work. I know the duct has to be insulated. Is there a "standard" size to the insulation in R value? I will be using metal ducting. What other precautions should I take with this installation? Any suggestion are welcome. I have done far too many installations of furnace systems but have always stayed away from the attic jobs, leaving them to the younger guys. But this job is for family.
    Thanks.
    Never give up; Never surrender!

  2. #2
    Join Date
    Dec 2005
    Location
    Cincinnati, Oh
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    5,183
    probably 1 1/2" foil back is code minimum.

    I'd go more if you could.

    Take some furnace/bailing wire with you. Spin the duct in the wire after you wrap it. It relieves the stress on the tape, and helps hold it together longer.
    "Better tell the sandman to stay away, because we're gonna be workin on this one all night."

    "Dude, you need more than 2 wires to a condenser to run a 2 stage heatpump."

    "Just get it done son."

    Dad adjusted

  3. #3
    Join Date
    Mar 2009
    Location
    Mount Holly, NC
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    3,415
    R-8 is required in US.

    it's 2"
    also, all fittings, and duct seams must be mastic sealed.
    also, the ductwork needs to be sized correctly by Manual J.
    The TRUE highest cost system is the system not installed properly...
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  4. #4
    Join Date
    Feb 2012
    Location
    VA
    Posts
    109
    if he is in Canada , you really need to consult some one who knows the R factor in Canada for your region. if you have to follow Canadian standards you should have some guidline to follow

  5. #5
    Join Date
    Dec 2005
    Location
    Cincinnati, Oh
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    5,183
    Quote Originally Posted by vstech View Post
    R-8 is required in US.
    Not in my neck of the woods.

    1 1/2" is code here.
    Across the river, it'll be r-8 in july.
    "Better tell the sandman to stay away, because we're gonna be workin on this one all night."

    "Dude, you need more than 2 wires to a condenser to run a 2 stage heatpump."

    "Just get it done son."

    Dad adjusted

  6. #6
    Join Date
    Dec 2011
    Location
    bedford ind
    Posts
    1,092
    3/8-1/2' bubble wrap is common here, or 1" fiberglass.

  7. #7
    Join Date
    Jun 2010
    Location
    Philadelphia PA
    Posts
    2,198

    Even in Canada

    make sure that the duct is not buried in or even sittting on top of the attic INSULATION. I understand there is even RH in CAN.
    Seems I remember some hot days in August competing in St Catharine's Henley Races
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

  8. #8
    Join Date
    Feb 2010
    Location
    Ontario Canada
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    1,341
    Quote Originally Posted by hvacvegas View Post
    probably 1 1/2" foil back is code minimum.

    I'd go more if you could.

    Take some furnace/bailing wire with you. Spin the duct in the wire after you wrap it. It relieves the stress on the tape, and helps hold it together longer.
    Really good idea about the bailing wire..Thanks.
    We do have heavy humidity here in the summer. A suggestion was made that the duct insulation should be the same as the attic insulation. In this case the attic will be insulated to R40. This seems to be the new standard for blown in insulation here.
    I like the idea of the 3/8 bubble wrap insulation. Maybe on top of the foil-back and this would insure that the duct is properly insulated.
    Anyone see any problems with that idea?
    Thanks I appreciate the help.
    Never give up; Never surrender!

  9. #9
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,060
    [QUOTE=trouble time;12651451]Really good idea about the bailing wire..Thanks.
    We do have heavy humidity here in the summer. A suggestion was made that the duct insulation should be the same as the attic insulation. In this case the attic will be insulated to R40. This seems to be the new standard for blown in insulation here.
    I like the idea of the 3/8 bubble wrap insulation. Maybe on top of the foil-back and this would insure that the duct is properly insulated.
    Anyone see any problems with that idea?
    Thanks I appreciate the help.[/QUOTE

    If not sealed air tight between the two vapor barriers it can condensate.

  10. #10
    Join Date
    Feb 2012
    Location
    Virginia
    Posts
    34
    In my neck of the woods the air handlers are in the attic about 70% of the time. Our code was changed in 2010 that all ductwork, regardless of location, has to be insulated to a value of R8.

    I definitely would check with the mechanical code for your area in Canada first. Im sure they aren't going to want you to go to R40 like the attic is. If so I'd move somewhere else instead of trying to wrap duct with 10" insulation.

    I also wouldn't put another layer of insulation over your original layer because it will trap moisture between the layers and present possible issue.

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