I am going from a flex-duct HVAC system to an all-metal duct system. What is the best way to insulate the ductwork?

Asked by John
Atlanta, GA

I am replacing the HVAC duct system in my attic. Going from duct-board/flexduct to an all-metal duct system. My question is -- I don't want to insulate the new system with fiberglass. My HVAC guy says he can glue reflective bubble wrap directly to the metal and tape all seams, rather than use fiberglass. Is this a good option? Are there better options for insulating ductwork? I have heard of using cotton fiber as regular insulation, but I haven't read about it being used as duct insulation. My goals are to insulate the ductwork so it doesn't sweat or lose heat. I also want to improve indoor air quality.


Danny Kelly

Answered by Danny Kelly

Charlotte, NC

Kelly McArdle Construction

October 11, 2010

Bubble wrap may help prevent condensation but will not help with heat loss / gain. 

I would recommend foil-faced duct insulation.

  • Most bubble wrap products have a R-value around 1.
  • You really want a product with an R-value of 8 in Georgia.

More importantly, prior to insulating, I would make sure all joints are sealed well with mastic and have the ducts checked for leakage with a duct blaster test.

The duct sealing is where you will get the added benefit of improved indoor air quality.


For more information:

Read Andrea Foss's Q&A "What's the best way to seal a 30-year-old AC duct system in an attic?"

Tagged In: insulation, ductwork

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