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Larry Leso
Sealing Ductwork

I am installing ductwork in my attic for central air, my home presently has radiant heat. A mechanical engineer designed the system, the duct sizes and locations and I am doing the ductwork installation. (An HVAC pro will install the unti and set things up.

I have rectangular duct, which comes in halves. Before connecting the halves together, I measured, cut and installed the takeoff boots for the individual room registers. Since I hadn't assembled the rectangular duct together, I found it easier to apply mastic to the exterior of the takeoff connections and foil tape to the interior of the takeoff connections.

After all the ductwork was up and installed, I started to think that the foil tape on the inside might fail at some point resulting in a flapping noise when the system is on.

Before I take everything down and redo it, does anyone have an opinion on this? The foil tape I used is UL rated 181 nashua tape and it's pretty tight. If I take it off, it's going to be a chore.


Re: Sealing Ductwork

Tape and seal, Tape and seal, I don't know how other people do it but the best way is tape your joints from the outside, then the Mastic goes over the tape. Never tape from the inside, you don't want anything to prohibit air flow, air flow is key. Good Luck!!:)

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