Hart & Cooley Type B Gas Vent Systems give you these important advantages: 1)Safety is assured by the double-wall, air-insulated design and locking joints. Properly installed, the vent cannot come apart through vibration, and offers protection against vent failure or fire hazard. Type B Gas Vent is designed for negative pressure applications and flue gas temperatures not exceeding 550° F for Category I appliances. 2) Durability is the result of high-quality materials and workmanship, with galvanized outer pipe and aluminum inner pipe providing protection against corrosion and external damage. 3) Simple installation is achieved with a complete line of adjustable fittings and various lengths of pipe. Curled ends lock together for stability and easy assembly. A full set of installation instructions are supplied with all caps and supports.