If we use a 6" round flex liner, and ovalize it for a foot or so where it passes through the damper, how badly will that impact draft? This is a project at a neighbor's house, he has an insert with a 6" round direct connect to the tile in the chimney right now, and we are replacing it with flex to the top. Will this 1-2' run of oval 6" ruin his draft, or will it be ok? Chimney height is 18' total.
-- MW
-- MW