Insulating basement HVAC Ducts

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  #1  
Old 08-06-08, 07:45 AM
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Question Insulating basement HVAC Ducts

I would like to insulate my HVAC ducts in my house. They are
6" diameter. I have a lot of 16" wide left over R13 paper faced insulation from other wall jobs. Can I use this to insulate these ducts by simply stapling it up into the joist space creating an insulated air pocket around the ducts with the floor joists and insulation? Will the vapor barrier on the insulation be a problem? Can I also wrap the big rectangular feeder ducts coming off the furnace with the same insulation?
 
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Old 08-06-08, 09:28 AM
airman.1994's Avatar
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If your basement is conditioned there is no need in insulating them. Duct wrap is the only good way to insulate duct work. You should purchase a duct wrap stapler and use the string tape that will match the insulation.
 
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Old 08-06-08, 01:41 PM
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My basement is not heated. It's unused space. I know duct wrap is good but I already have these fiberglass R13 rolls and the R rating is higher than duct wrap. I don't doubt that this fiberglass would insulate the ducts nicely, but I am concerned with possible condensation somewhere in the small air space I would create around the duct if I staple the insulation to each side of the floor joist and pack it up against the duct.
 
  #4  
Old 08-13-08, 06:22 PM
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Every single thing I've read about insulating existing ductwork says to wrap the ducts with insulation barrier on the outside (facing the attic not facing the duct.) And all the the pre-fabbed duct wrap I've seen has foil on the outside.

Why would you want air space around the ducts? The whole point of insulating ductwork is to keep the conditioned air inside the duct.

I wrapped mine tightly with thick foil faced fiberglass insulation and taped the seams together using high heat rated foil tape. This was after applying mastic to all the seams and joints.

Doing that, sealing all the attic air penetrations I could find as well, and blowing in more insulation was well worth the time and energy spent. I don't even want to think about how much conditioned air was escaping into the attic before, but from the drop in the electric bill it must have been a considerable amount.
 
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