How to insulate air ducts resting on rafters
Wrapping the ducts completely requires raising them off the rafters, a task you may be unprepared to do. This makes it difficult to properly address the ductwork, especially around the connections between the main trunk and the flexible duct.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
- 1Insulating only the three accessible sides with reflective bubble wrap and stuffing fiberglass underneathDid this help you?
- 2Sealing the duct to make it airtight with mastic and/or tape before adding insulationDid this help you?
- 3Wrapping fiberglass or standard insulation directly around the connectionDid this help you?
- 4Focusing on general air leaks in the home instead, which often have a larger impactDid this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“I just don't see how I can wrap them completely without raising them off the rafters which I am unprepared to do.”source ↗
“I could use some advice on how to address ductwork connections like these.”source ↗
“I was surprised to see such a difference between the main trunk and the flexible duct, especially around the connection.”source ↗
“What would be the best way to insulate these better?”source ↗
Where this came up
People with this problem also raised
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- 3How to fix an exposed HVAC duct after removing a drop ceiling
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