The diameter of the chimney flue liner must be at least what percentage of the fireplace opening?

The requirement that the diameter of the chimney flue liner must be at least 80% of the fireplace opening is based on established guidelines to ensure proper ventilation and efficient exhaust of combustion gases. This percentage helps to reduce the risk of smoke spillage, improves draft, and minimizes the potential for soot accumulation within the flue.

A flue liner that is too small in relation to the fireplace opening can lead to inadequate draft, resulting in poor combustion, smoke backdraft, and the increased risk of creosote buildup. These issues can not only affect the efficiency of the fireplace but can also pose safety hazards, including the risk of chimney fires.

Therefore, maintaining at least an 80% diameter ratio helps to balance the airflow, allowing for proper function and safety of the chimney system. This guideline is crucial for chimney sweeps and homeowners to follow for optimal performance and safety in metal, masonry, or prefabricated chimney systems.