What must the space surrounding a flue lining system installed within a masonry chimney not be used for?

The space surrounding a flue lining system installed within a masonry chimney must not be used to vent any other appliance, as this can create significant safety hazards. The primary function of a flue lining is to safely carry combustion gases from the appliance to the exterior. If this space were utilized to vent other appliances, it could lead to a backdraft of exhaust gases, improper venting, or dilution of those gases, which may cause the build-up of harmful pollutants and carbon monoxide within the living space.

Proper venting ensures that combustion gases escape effectively, protecting occupants and preventing potential fire hazards. Regulations and building codes typically require that each appliance have its own dedicated venting system to ensure functional and safe operation. This is crucial for maintaining proper airflow and preventing dangerous scenarios such as smoke or toxic gas infiltration into habitable areas.