DuraTech is a double-wall, all-fuel chimney system that is for use with wood stoves, fireplaces, furnaces, boilers, ranges, water hearts or other appliances fueled by wood, oil, coal or gas and zero-clearance fireplaces that are factory built. With a Thermal Insulation Blanket encased between dual walls, DuraTech chimney systems offer the optimum in safety and performance. DuraTech chimney systems feature an inner wall that is 25% thicker than competitive chimneys for an extra margin of safety. DuraTech chimney vent pipe requires a 2" clearance to combustible materials. Please Note: All Stove & Chimney Pipe is chosen and classified by the inside diameter. If your flue has a 6" Inside Diameter you will choose from the 6" Stove and Chimney Pipe categories.