This 3 Inch Pellet Wall Thimble With Air Intake from the PelletVent Pro series is a Type L Biofuel Chimney Pipe component and consists of the duralock system for a tight seal. Allows outside fresh air for combustion through the wall thimble without having to cut a second hole into the wall. Comes with an insulation ring to reduce air infiltration where the pipe slips through the thimble. The 2" diameter, 18" length flex hose expands to 5'. Clamps included. Can be used in US and Canada. Patented. Features: Type: Wall Thimble with Air Intake. Collection: PelletVent Pro. Type L Biofuel Chimney Pipe Component. Allows Outside Fresh Air for Combustion Through the Wall Thimble. Specifications: Overall Dimensions: 13" (L) x 13" (W) .