Use to add length to PelletVent pipe. 12" pipe adds 3"-10" of length when used with rigid sections of pipe. Adds length to PelletVent pipe PelletVent is an innovative venting system for pellet stoves and inserts PelletVent is UL listed for 1" clearance to combustibles in the USA PelletVent seams are factory-sealed on all elbows, tees,and fittings