Flex duct through an air barrier
In reference to maintaining the integrity of an air barrier, best practice requires all penetrations be properly sealed. Of course the most prevalent holes are manufactured by tradespeople, many of whom don’t understand the importance of the endeavor.
Specifically, when HVAC ducts penetrate the air barrier between conditioned and conditioned space, both code and Energy Star requires the annular space between the hole and the duct be air sealed.
Since there is a love affair with flex duct among the HVAC community, most of these penetrations is made with flex duct. And in all cases, I see the air sealing being made around the outer jacket of the duct. The two attached graphics even give a thumbs up on the practice.
Of course if the outer jacket is the air barrier, then why do ADC guidelines require sealing the inner liner to all duct connections? It is my understanding the outer jacket is simply to retard vapor diffusion.
I thought I recall that such penetrations are required to include a metal sleeve through the air barrier with flex connected on each end. Then, the air sealing would be effectively sealing to the air barrier of the duct.
Apparently, I am the only person in the U.S. who ever required this. Am I being just too picky? If the air barrier is also called a draft or fire stop, is it code compliant to seal the outer jacket of the flex duct to meet the fire stop requirement?
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