Product Description 4" x 12", 4VP-12, Pellet Stove Pipe. Type L vent tested and listed to UL-641 and UL-103 standards. Use to vent pellet appliances. Pellet vent cannot be interchanged with other manufacturer systems. Double wall and insulated design. Designed with a stainless steel inner wall and a 0.018 galvalume steel outer wall. 1" inch clearance to combustibles twist-lock construction . From the Manufacturer 4" x 12", 4VP-12, Pellet Stove Pipe. Type L vent tested, and listed to UL-641, and UL-103 standards. Use to vent pellet appliances. Pellet vent cannot be interchanged with other manufacturer systems. Double wall, and insulated design. Designed with a stainless steel inner wall, and a 0.018 galvalume steel outer wall. 1" inch clearance to combustibles twist-lock construction .