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Old 07-21-2013, 12:57 PM   #1
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Insulate duct work


I am in the process of finishing my basement, and I wanted to insulate the main trunk line of my duct work. The duct is 10" tall by 20" wide, and is attached on the underside of my I-joists, attached with hangers every few feet. Before I insulate I will check all the connections and brush on some mastic, along with check the existing foil tape over the seems.

My question is with regards to insulating the actual duct. Are there products out there specifically for insulating a box duct? It will be easy to insulate three sides of the duct, but the top can only be insulated between the joists, since top of duct and bottom of joist are pretty much butt up against each other. I was not sure if I should just buy batts of fiberlgass, and wrap tape around it to hold it in place, or if they make some kind of wrap for it. Should I also insulate the 6" diameter supply lines?

One article/video I found talked about insulating ductwork. It stated to use 1/2" foil faced polyisocyanurate and use that on the sides and bottom of the square trunk. Just tape the foil face to the trunk, and then use R-13 fiberglass on top of the trunk and then also use R-13 fiberglass and wrap the supply lines. Does this sound like a good way to insulate the trunk?

Any other info you can provide for insulating duct work would be great.

Thanks in advance,

Last edited by svaic00; 07-21-2013 at 01:40 PM. Reason: Added thought on how to insulate trunk and with what materials
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Old 07-21-2013, 05:39 PM   #2
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There is a vinyl backed fiberglass wrap that they make for ducts, that however does not make a good "finished" look. They make fiberglass duct board that has a layer of foil on the outside which when paired with foil tape can make a very spiffy looking insulation.

If you are enclosing the other metal ducts then I would go ahead and insulate them as well with the wrap.
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Old 07-21-2013, 10:19 PM   #3
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This is the product we used to insulate square & round duct when I used to work in HVAC,
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