Originally Posted by BridgeMan
For anyone who's interested--a 10" round has a net surface area of 78.54 sq. inches, while a 12" square has a net surface area of 144 sq. inches (not counting a slight rounding deduction at the corners).
Not quite the same. While the circular shape may be more efficient than a square in venting flue gases, I doubt the 10" can make up for the 54% net area deficiency it suffers compared to a 12" square.
Some people have a hard time with math! You are right ,if you have a regular size fire place you should have a 12 x 12 clay liner. The man should check and see if the clay liners are cemented in. If they were cemented, then that why they are cracked. Clay liners are suppose to just set on top of each
other so they can expand and contract with the temp change. The joints between the clay liners do not need to be sealed. Heat will not go out through the seems, the draft in the flue will draw air in through the cracks. Paul