Hi, Update 9/6/19 : I called Duravent; their associate told me that PelletVent Pro does not need additional insulation. He also mentioned that liner extending 1, or 2 feet above the masonry chimney should not impair the function of the liner. Original post: A first-time installer. The house came with 1970s fire place with masonary chimney, with a pellet stove insert. The chimney is inspected and is in good condition. Chimney height is 12 feet from hearth to the flue vent. A straight passage of 8' 2" from flue vent to top edge of the damper. I am planning to install PelletVent Pro rigid chimney liner for a pellet stove insert. The liner seem to have air insulation. - Do I have/need to add additional insulation blanket to it? - The masonary chimney rises about 5 feet above the roof and meets 10-2 rule. How many feet should I extend the chimney liner above the masonary chimney/flue? Thank you. Knight.