Hey, Admittedly my install is not bulletproof. I have about 14 feet from the bottom of my unit to the top of my chimney so probably like 12" of actual chimney liner. My insert heats fantastically, efficiently and burns cleanly. I try to burn good dry wood as best as I can. My problem is every time I open the door I get smoke in the house. And not just a a quick whiff, like it pours in the room. I have an offset box that attaches the insert to the chimney. I'm fairly sure the offset box is the culprit, but it's a necessary evil without extensive masonry work. Last year I replaced the offset box and used furnace cement to seal any suspicious air gaps. It had no improvement. Here's my question: will increasing the length of my chimney by 3 feet help? Here's my version of the math: 12 ft chimney + 3 ft (25%) increases draft by 25%. Is this correct? Will adding three feet really increase my draft and help with this? And if so what is the best product to transition a 6" SS flex liner to class A chimney (or whatever is best here)? Thanks so much.