Sometimes you may want to install a Class A chimney and you want the best draft possible. Instead of going out of the wall horizontally with the double wall pipe and using a tee, you may choose to go through your ceiling and the attic and out through the roof. This way your new factory built chimney will have no turns or bends, giving you less turbulence and the best draft possible in your Class A chimney.
If your ceiling is flat you just use a round ceiling support. If you have a vaulted ceiling and want to install a metal chimney through it, you need to use a Class A Chimney Square Ceiling Support. This box is secured to the rafters and maintains the minimum clearances to combustibles.
The bottom of the support box needs to be exposed by at least 2 inches on all sides. If your ceiling has a steeper pitch you need to install a taller support box. The trim on the support box is made from two separate pieces that slide over each other and adjust to the pitch you may need.