Wrapping hot air ductwork

[Junkman]

I was talking to the ductwork installer today, and he said that they no longer wrap the ductwork, since wrapping it doesn't give much insulation. From memory, I think that he said the wrap was a R-6, and that the cost of the material and labor made it prohibitive cost wise. He suggested that if I want to wrap it myself, that I should use bubble wrap with the silver outer layer, and to use spray glue to hold it onto the ductwork. Looking for additional opinions on this matter. thanks Junk

 

[Jess]

Tape all the seams with foil tape. That will reduce a large amount of loss in a system and either keep the heat or cool in. Cheap and worthwhile fix if its not being done at installation.

 

[NUTTSGT]

When I ran the duct in the garage this past spring, I bought some flexible duct with teh intention of running the sheet metal duct through it. It would have been fine but I wasn't able to do it in the confines of the attic. I cut it apart and wrapped the duct work after it was installed. Once that was done, I wrapped that with bubble wrapped and used foil tape to seal that.

http://www.garagejournal.com/forum/showpost.php?p=5669856&postcount=2162

 

[Junkman]

Some of the ductwork is the flexible fiberglass with a plastic coating. Would you wrap those also? I am thinking of having the attic roof rafters sprayed with insulating foam, and at the same time, have them spray foam all the ductwork.

 

[csp]

Is the ductwork in the same space that's heated (conditioned space)? If so, you don't need to do anything other than seal the seams.

 

[ambenz]

My ducts running in the basement for discharge in the main floor were never insulated.
I would loose a bit to the basement space as it wasn't finished.
Now that I added a drop ceiling and a few vents to heat the basement, the heat loss off the un-insulated ducts get "trapped" between the drop ceiling and main floor creating a warm floor through out the main floor! Kind of like a radiant heated floor. So no big issues in my case.

 

[NUTTSGT]

Some of the ductwork is the flexible fiberglass with a plastic coating. Would you wrap those also? I am thinking of having the attic roof rafters sprayed with insulating foam, and at the same time, have them spray foam all the ductwork.

I think I'd becareful of that. I'd be worried that the spray foam might expand and push in the the flexible ductwork creating internal restrictions.

 

[tab2]

Ductwork that is not exposed to the ambient air it is conditioning must be insulated in MA commercial buildings. Does it help? I can't tell you that, but it is what is enforced by inspectors here. It is typically 1-1/2" fiberglass based with a foil face. I'm unsure of the R value. Exposed ductwork does not have to be insulated.

I think using foil tape and duct seal is more important to not lose any conditioned air. Spray foam is expensive, I don't think it would be worth it on the tin.