I have a Vermont castings vigilant in a fireplace with about 18 to 24 inches of stove pipe going up the chimney. The stove actually sits on the hearth. The flue is 13 x 13 tile lined all the way up. I have used it this way for 6 years. Chimney is about 25 to 30 feet, in the middle of the house. Do I need to install flex liner or can I continue using it the way it is. Chimney is part of a double chimney, one for upstairs (Jotul c550) which has a liner. Chimneys are separate from each other. What might be the cost of 8" ss flex liner ? Best place to buy? Price from Northern supply is around $500. Thanks for the advice.