Kitchen range, dryer, bathroom fan, and other exhaust ducts that don't vent combustion air can be air sealed with relative ease. Besides making the ceiling penetration airtight, it is also important to air seal the duct itself to prevent warm, moist air from venting into the attic. All mechanical air ducts (both supply and exhaust) running through the attic should also be insulated in order to avoid condensation within the duct and reduce heat gain into the attic, which can be an issue in colder regions where it may contribute to ice damming. Flex duct that is not insulated should be replaced with insulated ducts, and rigid ducts should be covered with an insulation sleeve.

This air sealing procedure is for a range or other exhaust duct that penetrates the ceiling without a framed shaft.