Vent Pipe Thimble

Just looking for information about vent pipe thimbles. Do these take the place of the 1" clearance requirement as long as it is used with a B (double wall) vent pipe? I can’t tell from my picture if this is a single wall that goes into a double wall thimble? Any help or comments are appreciated.

The thimble still satisfies the clearance requirement, it doesn’t take the place of it or remove it in any way(I’m not sure if that answers your question or not). It’s simply a way of having the needed clearance without a big gaping hole in the ceiling or wall.

So I guess it is safe to assume that there is a 1 inch clearance behind the thimble flange? Also does it appear that this is a single wall vent going to the thimble?

I wouldn’t call that a thimble, I would call that a collar. You should not use a thimble for B vent (which that is) through a ceiling, you need a firestop. That collar is probably supposed to be a firestop, but may not be approved, check your ahj. B vent firestop is usually a flat sheet metal plate.


Ok thanks your right, with a collar you can’t really tell if there is a 1" clearance to the drywall. A firestop would be a better option thanks for the picture.