How far must clay flue liners extend below the lowest inlet in masonry chimneys?

Clay flue liners must extend a minimum of 8 inches below the lowest inlet in masonry chimneys to ensure proper functionality and safety. This requirement is established to prevent the potential for smoke and combustion gases to escape from the flue at the lowest inlet point, which could lead to unsafe conditions, including fire hazards and improper venting of fumes. Extending the liners sufficiently also helps to protect the masonry structure from deterioration caused by exposure to high temperatures and corrosive byproducts of combustion.

While other measurements are specified for different scenarios or materials, the 8-inch extension is the critical standard to follow for clay flue liners in order to maintain both the effectiveness and safety of the chimney system.