DuraBlack Increaser – 8″- 10″ The DuraBlack 8″-10″ Single Wall Stovepipe Increaser is a component that is used in a typical venting installation. The DuraBlack increaser is used to increase from a smaller appliance flue outlet to a larger diameter chimney or stove pipe. Features: Type: Increaser. Used in a Typical Venting Installation. Use to Increase from a Smaller Appliance Flue Outlet to a Larger Stovetop Diameter. UL Listed. Specifications: Overall Dimensions: 7″ (H). Size: 8″- 10″.