I have a ceiling mounted exhaust fan that has a substantial (2-4" air gap along the sides after it was installed such that when it is running a lot of the air just gets pushed back around the sides of the fan.

I'm thinking of applying some spray in foam around the fan to get a better seal around the fan to prevent this. That foam is some nasty stuff and I don't want it just dripping back down on me as I apply it overhead into the gap.

Is there a method for spraying foam into an open space overhead safely to avoid a big mess underneath?

  • Sure - first, patch the ceiling correctly. Presumably drywall? – Ecnerwal Sep 18 '19 at 23:56
  • Tile. It is a shower ceiling. – JohnFx Sep 19 '19 at 0:02
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    Hold on just a second - a properly installed exhaust fan should not be pushing any air at all into the ceiling space, so it shouldn't make any difference if there's a gap around the fan. The exhaust should be run directly from the fan's outlet into ducting which leads outside the house! – brhans Sep 19 '19 at 0:04
  • There is a duct leading outside it just doesn't have any direct connection to the fan. – JohnFx Sep 19 '19 at 0:36
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    it really needs a direct connection. – JACK Sep 19 '19 at 0:39

Rather than using that spray foam you'd be better off getting a sheet of Styrofoam and cutting it to fit the opening around your fan. Make a template out of cardboard and then trace it on to the Styrofoam, cut it out and fit it into the opening. You can then caulk around it sealing it further. Now, you need to make that direct connection to the duck you said was already in the attic. You're looking for trouble venting hot, moist air directly into your attic/crawlspace.

  • Thanks. That's what I'll do! – JohnFx Sep 20 '19 at 15:54

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