Should I fill the gap between sleeve and chimney structure?

Question

Currently, my chimney is brick and has a 8" type B metal duct pipe coming out of it as a sleeve, which exhausts home heat and water heater appliances.

The chimney was dormant for many years before I started using it after some remodeling and reengineering home infrastructure. However, I didn't fill the space between the masonry and the sleeve. And maybe some 18" into the chimney from the top of bricks starts the old sleeve, which was ceramic I believe or made of a similar material as roof tiles.

Should I fill the space on top of my chimney between the sleeve and the brick structure with something, as was done with my neighbor's chimney?

Answer 1

I do not know if it is necessary to actually fill it, but as a minimum I would use metal to create a collar to keep it stationary and to keep the weather, bats and other critters from causing future headaches.

Answer 2

A mason could add a cast-in-place chimney cap to that to seal the gaps between the brick and the metal flue.

Answer 3

That was installed incorrectly the chimmny should have been built up to the top of the flue pipe then a flat plate should have been installed with the pipe comeing through it or a critter cap installed as a fourth generation mason that is the proper installation