The Ontario Building Code | Separation of Flue Liners
9.21.4.9. Separation of Flue liners
(1) Flue liners in the same chimneyshall be separated by not less than 70 mm of masonry or concrete exclusive of liners where clay liners are used, or 90 mm of firebrick where firebrick liners are used.
(2) Flue liners referred to in Sentence (1) shall be installed to prevent significant lateral movement.
In Plain Language
Where a chimney has multiple flue liners, they must be separated as set out in this article, preventing heat or gases from one flue from affecting an adjacent one.
This is a plain-language summary of the 2012/2017 Ontario Building Code text above, for general understanding only and not a substitute for the Code. Always confirm current requirements against the 2024 edition (O.Reg. 163/24) or a qualified professional before construction.