In masonry chimneys, how far should clay flue liners extend above the enclosing walls?

Clay flue liners in masonry chimneys should extend at least 8 inches above the enclosing walls. This is a critical requirement that helps ensure proper ventilation of combustion gases and prevents downdrafts from entering the chimney. The extension helps maintain a sufficient height above the roofline, which enhances the chimney's ability to draw air upwards and exhaust smoke and gases effectively.

By extending this distance, the flue liner minimizes the risk of interference from roof overhangs, trees, or other structures that might obstruct the upward flow of the gases. It also plays a role in reducing the chances of chimney fires and increases the overall safety and efficiency of the masonry chimney system. Various building codes and safety standards support this requirement, emphasizing its importance in the design and construction of masonry chimneys.