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I just installed a new gable fan to exhaust hot air from my attic. Due to unevenness in my studs and gravity pulling one side of the fan lower than the other, there are small gaps (ranging between 1/8" and 1/2") between the external-facing edge of the cylindrical fan housing and the studs that it's mounted to. The fan comes with black plastic covers that are supposed to prevent gaps but they're not thick enough to fill the gaps. So I'm getting a lot of hot air pushed through those gaps back into the attic instead of exhausted to the outside.

I'd like to come up with a good sealing solution. Here's some criteria that I think make sense:

  • Can withstand years of fan vibration without breaking down
  • Can fill gaps up to 1/2"
  • Ideally, would help to dampen vibration and sound of the fan which can be heard (albeit softly) in my daughter's bedroom which is one story below the gable.
  • Not an obvious code violation (I'm in California) or safety hazard

Here's a few ideas I've heard:

  • wrap with neoprene (like a wetsuit)
  • wrap the gap with flexible foam with a circular cross section, like a thin pool noodle
  • one of above, and then secure with duct tape (or perhaps the high-end metal duct tape which might be more durable?)
  • one of above, and then caulk (and if so, what kind of caulk?)

What would you do?

EDIT: here's a picture. I know that I'm supposed to fasten the black covers over the mounts, not under them, but I'm loath to go back and undo all this work and potentially ruin the black covers in the process.

enter image description here

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  • 2
    It's pretty difficult to picture the situation right now, some photos would help!
    – MiG
    Commented Apr 2, 2022 at 10:54
  • Are you looking to fill the gaps from the inside of the attic or the outside?
    – FreeMan
    Commented Apr 2, 2022 at 13:10
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    Are the gaps able to let rain/water in(think of rain with a high wind before saying no)?
    – crip659
    Commented Apr 2, 2022 at 13:38
  • Photos added. @FreeMan - inside.
    – Justin Grant
    Commented Apr 2, 2022 at 21:27
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    I like the neoprene idea best btw. Reducing transfer of vibration will be more difficult, but you could try putting an extra layer of rubber underneath those 'feet'. And depending on what the other side of that fan looks like (do you also have a zoomed out shot?) creating a short funnel with that neoprene (maybe attached to a metal ring at distance) will reduce transfer of sounds a bit as well.
    – MiG
    Commented Apr 6, 2022 at 19:44

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Stud framing should be nice and flush, but rarely is. If you have an application that requires a really flat surface, you have to make it so.

I'm not sure what that silvery piece is (looks like plastic cardboard), but this is what I'd do:

  • Take down the fan and remove that backer piece
  • Shim the wall until you've got a flush surface
  • Remount the backer piece and fan
  • Attach the shrouds
  • Caulk as/if necessary

Another option would be

  • Cut a piece of plywood/OSB roughly the same size as the silver backer board
  • Cut a hole in it
  • Get it sealed to the studs by adding new pieces of 2x4 as necessary to make a seal
  • Use something like foam sill seal between the new pieces of framing and the plywood/OSB to help dampen vibrations
  • Mount the fan to the plywood/OSB now that you've got a flat surface.
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