Duct insulation recommendation

[MikeC55]

I'm installing an air retrun duct for 3 ton central AC system (that only had half of return volume it should have). It's in uninsulated attic space so I will need to add duct insulation to the sheet metal (rectangular) ducting. I see some rigid fiberglass board and many flexible foam/foil products. The return plenum is tight between 16" OC ceiling joists so not much clearance for insulation on those sides. I was thinking maybe spray foam in those areas and 2" (R-8) fiberglass for all else. The existing ducts have what appear to be 1" thick fiberglass (semi-rigid). Any thoughts on best way forward?

 

[fitter30]

Some good videos on u tube. Foil covered fiberglass for radiate heat. Don't use duct tape. Use a quality foil tape made for duct wrap.

 

[86turbodsl]

I like spray foam on ductwork. Serves as sealing at same time, avoiding tape installation costs.

 

[mike93lx]

Some good videos on u tube. Foil covered fiberglass for radiate heat. Don't use duct tape. Use a quality foil tape made for duct wrap.

Duct tape is fine.

Duck tape is not

 

[MikeC55]

How do you get uniform coverage with foam? It seems like it would be difficult. The only foam spray I have expereince with is the stuff you use between window/door frames and (wood) structure. Does the insulating foam expand less (making it wasier to control coverage)?

 

[mike93lx]

How do you get uniform coverage with foam? It seems like it would be difficult. The only foam spray I have expereince with is the stuff you use between window/door frames and (wood) structure. Does the insulating foam expand less (making it wasier to control coverage)?

You don't need foam to be even, you just need enough everywhere.

I wouldnt use canned spray foam for this. Blanket insulation is made for the purpose and is removable. Foam is not

 

[86turbodsl]

There is spray foam that is specific for spraying on a surface. My house ductwork is sprayed. It's not the same as the foam in a can.