Duravent 4GVL90 4-Inch Adjustable 90 Degree Type B Gas Vent Elbow Twist locks into place: No sharp tabs to bend into slots, easy installation with no mechanical fasteners required Firm, lock-tight connection: DuraVents innovative system DuraLock allows for a lock-tight connection Engineered to heat-up rapidly: Type B gas vent remains hot during the operation of the appliance with minimal condensation in the appliance and vent system Limited lifetime warranty: The best warranty in the industry, 15-year 100%, 15-year and up 50%, gives the installer and homeowner the greatest peace of mind in a quality installation Designed to meet the rugged demands of the job site with a recessed inner wall