the unit can be connected to a flue that is within cross sectional value no more than 2 times that of the flue collar on the stove. 2 times piR squared. the "R" is radius so if a 6 inch round is used its radius is 3 (or half the width) 4 is radius for 8 inch round. so piR sq. is for a 6 inch round (3 X 3) X 3.14, or 9 X 3.14.
on a square flue you simply go length X width so a 6 inch square would be 6x6 or 36 sq in. say a flue is 6 X 9 would be 54 sq in.
connecting to an 8 inch round flue is fine. bigger than that would be an issue. you look at cross sectional value, which is basically how many square inches of space. a 6" flue would be 28.26 sq inches (3.14 X 9) or (3 times piR sq.) now an 8 inch round would be 50.24 (3.14 X 16) or (4 times piR sq)
so at 28.26 X 2 (56.52 sq in) you have your maximum cross sectional value for a 6 inch flue'd appliance the 8 inch round is within the size parameters allowed to connect to any woodstove with a 6 inch collar unless the manufacturer SPECIFICALLY states you can only use a 6 inch flue. we do not make that specification.
so long story short yeah you can hook that 13 up to an eight inch flue. just thought it would be neat to throw the math out there for folks to see how to calculate cross sectional values on a round flue.
Awesome reference Mike, all that and your a Steelers fan as well......LOL. Seriously though, your products are great and your customer service is outstanding. CR250Rider you would do well for your $$$$investment with the 13.