Jason, My fireplace chimney is very unusual since the flue is so far forward and the smoke shelf or smoke chamber is so deep. There is no place to put the Chimney Balloon that has parallel walls before the 8×18 tile flue. Do you see any options that may be easier to install in according to my diagram? – JA
Dear JA: This is not an easy install since your lowest point with parallel walls will be the flue tile above the smoke shelf. Looks like the 18″x 8″ location would be best with an HEK extender handgrip. The smoke shelf juts out so much that the CB handgrip would get in the way of it, if trying to put the CB into the chamber just above the smoke shelf. – Jason
Note: In this case, a Custom 18×8 with an HEK extender worked very well and was easy to install since the flue was only 13″ above the smoke shelf ledge.