Feeling dumb here. Finishing up a remodel and have a Broan InVent fan with ~1/2" lip around the bottom. The instructions indicate attach the fan to the joists with the bottom 1/2 or 5/8" down and then "install the drywall".

Given that I didn't buy any of the magic stretchable drywall to go around the lip and snap back snug to the body, I have no idea of how that would be accomplished without cutting the hole at the outer perimeter of the lip which, in my thinking, is too big of a gap and makes no sense as the lip would provide no value. It also would not enable me to seal the outer gap so that is a no go in my specific air-tight/sound mitigating construction goals.

I can't bypass this issue of cutting the drywall tight to the body by just doing the install as a retro fit as the exhaust pipe is rigid so I couldn't pull it down.

The only thing I can think of at the moment is to bend the lips/flange up (or cut them off) as they seem to only be there for retrofits (two other fans I installed did not have any of these lips). Thoughts?


  • 3
    Your question is a little confusing. Yes you mount the fan to the joist. Then you carefully measure and cut the hole in the drywall and install the drywall. I don't know anyone that can get that hole perfect without some sort of gap. Once the grill is on you won't see the gap. Depending on what's on the other side of the drywall and how big the gap is you fill in the gap with the appropriate material. If you can't move the pipe replace a few feet with flex pipe. Dec 16, 2021 at 5:24

1 Answer 1


In a retrofit, where the ceiling drywall is already installed, the flange at the bottom of the box goes against the existing drywall. The flange sets the installation depth, and the drywall cutout will be the size of the housing box.

In a new installation, standoff tabs in the housing set the installation depth from the joist bottom, and the ceiling drywall is cut to the outer perimeter of the flange. The drywall cutout will be the size of the flange edge, and the drywall does not tuck behind the flange.

When installing a new ceiling drywall panel at the fan, loosely screw it to the joists without burying the screw heads and cover the ceiling fan housing. You can't tighten the screws because the housing will keep the drywall near the box 1/2in off the joists. Poke a hole with a drywall saw somewhere within the box perimieter, cut to one of the sides, and carefully cut over the flange to the outer side. From there, cut around the outside of the flange, which is the cutout perimeter for the fan, using the flange's edge as your guide. It's not visible in the beginning but you can "feel" when the saw rides against it. You can do this with a drywall saw or a power tool like a spiral saw.

In both cases, new and retrofit, the grill will loosely seal off against the flange, regardless whether the drywall is behind the flange (retrofit) or butted to the drywall (new install).

None of this is mentioned in the manual or in the video, which I find baffling.

  • Well, that obviously makes two of us that find it baffling. Had they simply mentioned cutting it out to the outer flange, whereas the retrofit you cut it to the body, that would have made it much clearer. Really must made it look like I would have to figure out how to tuck the drywall somehow. The last two fans I installed did not have a flange so there was no confusion, just cut it tight to the body. Given I have to seal it for air and sound, I think I'll just have to bend the flips up flush to the body.
    – Mike P
    Dec 16, 2021 at 6:14
  • 1
    @MikeP I was wondering about the exact same thing with my fans, thinking I'd go for a satisfying neat tight flange fit...
    – P2000
    Dec 16, 2021 at 6:17

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