chimney liner question

[ledwards]

For a 20’ chimney that has a 7" terracotta liner, what would be better, an insulated 5.5-inch liner or an uninsulated 6-inch liner?

 

[MountainStoveGuy]

well, i would first want to find out what the condition of the terra cotta liner is. Most are cracked. Technically, UL1777 states that liners have to be insulated to be installed per there listing. But NFP211 states that liners should not be any smaller then the flue collar. So, in reality, i would insulate a 5.5 as first choice if the clay liner is in bad shape. If its in good condition i would go 6" un insulated. It will be easier to pull. I would also recommend rigid liner, its thicker, drafts better, and its easier to clean.

 

[Hogwildz]

well, i would first want to find out what the condition of the terra cotta liner is. Most are cracked. Technically, UL1777 states that liners have to be insulated to be installed per there listing. But NFP211 states that liners should not be any smaller then the flue collar. So, in reality, i would insulate a 5.5 as first choice if the clay liner is in bad shape. If its in good condition i would go 6" un insulated. It will be easier to pull. I would also recommend rigid liner, its thicker, drafts better, and its easier to clean.

Double wall rigid is insulated too.