I want to connect this old bathroom fan to a new roof vent via an insulated duct.

Of course, first I need to get rid of all the rotten insulation that was waterboarded with endless moisture from the bathroom over the years.

But assuming that's taken care of, my focus is on installing the duct correctly. The duct connection to the roof vent looks obvious, but I'm not sure how the insulated duct would connect to the fan.

Here's a closer shot of the fan exhaust.

Yes, please try to look past the moldy goodness. There is a square flap inside of the round exhaust collar. When the fan isn't running, the flap rests inside the collar. And when the fan is running, it is pushed out slightly at an angle by the air flow as shown in this photo.

How do I connect this to the insulated duct? Do I just slide the duct over and around this round collar and fasten it with foil tape and a duct clamp? Or do I need something to sit in between and mate the exhaust port to the insulated duct, like a metal duct elbow?

  • is the old duct rectangular metal
    – Traveler
    Jun 28, 2022 at 3:42
  • @knowitall - There was no old duct. The roof vent is new, and the fan was (and still is) just blowing air into the attic insulation. Jun 28, 2022 at 3:46

1 Answer 1


You slide the pipe over and make sure that flap (s back draft damper is working) good job at finding this and properly venting all that moisture out of the building. A long zip tie on the inner plastic to the round section is what I usually use, if the connection is tight tape is not needed but can help seal if the zip tie is not a good seal. Once the inner plastic is sealed pulling the insulation over and zip tying or tape makes it look like a professional install.


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