Type HT listed, factory-built, all stainless steel chimney section. if connecting to Chimney Extension (p/n10508), use the 8″ Chimney Band Clamp Kit (p/n 4518) at the joints. Sections are four feet long. The 8″ Chimney Ring (p/n 1200037) is required for Classic furnaces with the square chimney box (requires welding to the furnace).