Been doing lots of research here on hearth, lots of long old threads about diameter and flow and velocity and so on. Here is my question. I have yet to fire my new WS IS, it's on the hearth and before I get into the season where I need it id like to at least meet most requirements set before me buy Woodstock. 15 feet of 6" chimney from the collar of the stove. I measure mine at 12 feet from the collar this is with a 30" rise from the stove, a 90 degree elbow, about 18~20 inches of horizontal 6 inch all in black single wall. Feeds through a masonry thimble into a 7x7 clay lined masonry chimney that stops at a total height of around 12 foot ( from stove collar). With the elbows and oversized 7x7 clay I'm fearful that my "wing and a prayer" will leave us cold this fall. My immediate thought was to line with the correct size, but I really want to add 4-5 feet on top of where my chimney stops. Is there any way to attach a section of double wall on top of the cap that finishes of the liner kit, like where the cap is supposed to fit. Or any suggestions? I'll try and get a picture in the morning if that helps. Btw I don't want to extend my masonry chimney any higher, it's already broken off and fallen on the roof once about 15 years ago in a hurricane. I don't want too worry about that every time we get a stiff breeze. It was rebuilt but this time they made it noticeably shorter.