One of my projects this winter is to air seal and upgrade the insulation in our house. I got to thinking about upgrading the insulation of the duct work as well since its located in the attic. The main trunk line is made out of the fiberglass insulation board that has foil on one side and then its the typical round insulated slinky duct to the outlets. The main trunk is square and is installed in the web of the truss work. When I bought the house years ago one of the things I did was to use the mastic in the tubs to seal all the taped joints. I am pretty sure it is made with 3/4" or 1" board and I think they changed requirements to something like 2" thick. Any ideas on how to improve the insulation of the truck line? Wrap it with some kind of insulation? The smaller round duct I can just buy new as I am guessing they have that available in a higher R value. And at the end of the day is this something that's going to make a noticeable difference?
Improving Duct Insulation
- Thread starter gregs
- Start date
Air sealing made a huge difference in our house (built in 1984). I think that will be the best ROI.
I am more concerned about the fact that the main trunk is made from fiberglass board than metal. It’s probably fine but I’d still be wary of it eventually releasing fibers into the airstream (though I have no data either way).
I am more concerned about the fact that the main trunk is made from fiberglass board than metal. It’s probably fine but I’d still be wary of it eventually releasing fibers into the airstream (though I have no data either way).
mrbill55
Well-known member
Not just the insulation of the ductwork, but the sealing of the seams on the ductwork is what will drop your energy bills.
Bill S.
That’s around the same year of our house. The air leaks I’m guessing are substantial from what I have seen. As for the fiberglass, I have seen companies advertising sealing duct work from the inside. So that could be an option if I think it’s a problem but I don’t know that it is.
I will check everything again, but the mastic work I did years ago still looked ok the last time I was up there.
danski0224
Well-known member
There's no easy way to increase the R value.
IIRC, code now is R8.
That's only achieved when properly installed. Good luck with that.
I believe flex duct is available as R10, but I've never seen it on a jobsite.
The attic is what, R42 or something like that? You'll never get the ductwork that good without cubic dollars.
Depending on your climate, adding more insulation on the other side of the vapor barrier (the foil) can cause problems.
Your best path is to encapsulate/insulate the attic space and make it part of the indoors.
IIRC, code now is R8.
That's only achieved when properly installed. Good luck with that.
I believe flex duct is available as R10, but I've never seen it on a jobsite.
The attic is what, R42 or something like that? You'll never get the ductwork that good without cubic dollars.
Depending on your climate, adding more insulation on the other side of the vapor barrier (the foil) can cause problems.
Your best path is to encapsulate/insulate the attic space and make it part of the indoors.
billconner
Well-known member
I agree completely. Ducts and HVAC gear in unconditioned attics (or crawls or unconditioned anything) is always a poor choice.
acer66
Well-known member
This and make sure that your ducting does not make any unnecessary twists and turns.
There is no way to make it conditioned space. I will definitely go back over everything and check for leaks but it sounds like trying to upgrade the insulation is not practical. So I can scratch that off my list. One of my other air sealing questions is what to do about old ceiling mounted can lights? I only have 4 in the living room, but they are the old swivel kind. I am guessing there has to be a new LED replacement that can be sealed up better in the attic?
danski0224
Well-known member
There are containers that look like big flower pots made to encapsulate can lights. Will have to use an LED bulb so the heat limit doesn't trip.
brianpgriset
Well-known member
Here is an interesting article on spray foam encapsulation of ducts. Ive wanted to do this but I’ve prioritized traditional air sealing methods first.
basc.pnnl.gov
Encapsulated Ducts | Building America Solution Center
Guide that illustrates how and when to encapsulate ductwork in unconditioned attics, increasing the R-value of duct insulation, mitigating condensation issues, and reducing air leakage.
Wiz02
Well-known member
Great link, thanksHere is an interesting article on spray foam encapsulation of ducts. Ive wanted to do this but I’ve prioritized traditional air sealing methods first.
Encapsulated Ducts | Building America Solution Center
Guide that illustrates how and when to encapsulate ductwork in unconditioned attics, increasing the R-value of duct insulation, mitigating condensation issues, and reducing air leakage.