When is a chimney considered to be an exterior chimney?

A chimney is considered an exterior chimney when 50% or more of its structure is located outside the building. This definition is crucial in understanding building codes and regulations, as it affects heating efficiency, structural integrity, and safety measures associated with chimney installation.

When more than half of the chimney extends beyond the exterior wall of the building, it is subject to different considerations than a chimney that is primarily enclosed. This distinction can lead to different requirements related to insulation, support, and clearance from flammable materials. In contrast, if a chimney has less than 50% exposed, it is typically classified as an interior chimney, which adheres to different guidelines and tends to have different performance characteristics concerning heat loss and combustion safety.

Understanding this classification helps ensure proper installation and maintenance of chimneys for both efficiency in venting combustion gases and compliance with safety standards.