Insulating existing rectangular duct trunk supply

5 years ago

I am starting a basement project and want to insulate the existing rectangular duct that runs down the center of the basement (photo attached). Current plan is to build a bulkhead around the duct when I finish the basement. I would like to insulate this rectangular duct before I close it in. It is currently un-insulated, the top and bottom and one of the sides are mostly clear, but one side is against the main horizontal support beam for the house (On that side I might be able to squeeze some very thin foam board insulation in between the duct and the beam).

I have been searching the internet for ideas to insulate this rectangular duct. The link below looks to be the best option for what I am trying to accomplish. It involves installing 1in foil backed foam board

https://www.youtube.com/watch?v=s1EK8dMiZj8&feature=emb_logo

Any ideas or feedback is appreciated. Thanks

Featured Answer

Seabornman

5 years ago

I used duct wrap insulation, sealed with aluminum ductwork tape. It worked fairly well. Some spots you just can't get to, but it's not critical.

Sort by:Oldest

Comments (7)

mike_home
5 years ago
When I finished my basement many years ago I did not cover the main duct with insulation. What I should have done was apply mastic seal to all the joints. The duct is running through conditioned space so there in not going to be much loss in heat loss or gain. There is no harm in adding insulation. I highly doubt you will see in any change in your heating and cooling costs.
Related Professionals
Ithaca General Contractors · Reno General Contractors · Nashville Home Remodeling · Williston Home Remodeling · Syracuse Bathroom Remodelers · Las Vegas Bathroom Remodelers · Sebring General Contractors · Topeka General Contractors · Zanesville General Contractors · Nashua General Contractors · Plattsburgh General Contractors · Brattleboro General Contractors · Saint Cloud Cabinets & Cabinetry · Grand Junction Cabinets & Cabinetry · Eugene Cabinets & Cabinetry
Elmer J Fudd
5 years ago
I agree with mike_home insofar as the importance of sealing all accessible duct and plenum joints and connections with painted on mastic or, at a minimum, real mastic tape. Not standard garbage "duct tape". It works well and makes a big difference.

Do the same with return ducts as well as supply ducts.
Andrew
Original Author
5 years ago
Thanks for the feedback, agreed - I plan to seal (mastic and high quality/heavy foil tape) all seams as well.

Seabornman - Were you able to access all 4 sides of the duct? I may go the duct wrap insulation wrap as well, but I'm trying to figure out how to hold it in place on the bottom when the one side is against the beam.
Seabornman
5 years ago
It's been so long I don't remember. Buy the good aluminum tape. The cheaper stuff doesn't stick as well. Use a plastic spatula to rub it in. If you use your hand you'll get all cut up.
Bruce in Northern Virginia
5 years ago
What is the purpose of your insulating a duct running through conditioned space? Is it for noise reduction, or some other reason? I think sealing it well is more important than insulating it.

Bruce
Mini-Split Warehouse
5 years ago
Insulating HVAC Ductwork.

https://www.heating-air-conditioning.net/

When insulating HVAC ductwork, use a foil, faced fiberglass insulation with an R-6 or higher R-value. Use the type of metallic foil duct tape recommended by the insulation manufacturer to seal and hold the insulation in place.

Make sure the foil surface of the insulation is free of dust before applying the tape. Peel the paper backing off the tape as you apply it to prevent the tape from sticking to itself.

If your existing duct insulation is in fairly good condition, an additional layer of duct insulation can be applied over it. If the old insulation is in poor condition, remove it and replace it with new insulation.