Air Leak Around Cathedral Ceiling Support Box

[Ferg_1977]

Hi all,
Pulled the pine trim off from around our chimney box. Pics below.
We have significant air leakage around our cathedral ceiling support box.
When the dryer and/or bathrooms exhaust fans are running it pulls a crazy amount of stale attic air into our living room.
Confirmed by doing a smoke test around the perimeter.
Even if just the furnace or AC are running it’s pulling attic air into the living space.
How can I safely seal this up?
Leaning towards great stuff fire block spray foam between the exterior of support box and the t&g pine boards.
All advice welcome.

 

[Ferg_1977]

This is where the air leaks in around the perimeter of the unsealed ceiling box and is drawn into the living space when the dryer or exhaust fans are running.

 

[kborndale]

Doesn't look like much of a gap, couldn't you just silicone it?

 

[begreen]

Silicone should do. Are there any drafting issues in the winter when fans or dryer are running?

 

[Ctwoodtick]

I was thinking silicone too. I have imagine this is normal, especially if rest of house pretty tight.

 

[gthomas785]

Silicone or closed cell spray foam, or even some draft blocking tape would probably work.

 

[joop]

silocone,looks neater

 

[gthomas785]

whatever is used would be covered by the trim ring