I am constructing a chimney for a (my home) wood stove using an 8" flue inside 16" block. Without using an adapter pipe, how do I connect the round and square pipes where the horizontal 8" round flue meets the vertical 8" square so as to have the best structural support for the column and air tight seal? Is there a diagram online you can point me to? My supplier says they stopped selling the adapter since no one buys them. With all the concern about chimney fires I want this done to code...