Keystoker K-8 Chimney Size?

Does anybody know what the recommended chimney size for a Keystoker k-8 boiler is? It has an outlet of 9" diameter or 63 sq. in.

I am planning to build a chimney and use Nominal 8 x 13 tile flues. Height will be about 25 feet. The effective area of the flue is rated at 70 sq. in. USABLE area.

I read that the chimney must be at least the same area as the flue outlet but not more than 3 times larger.

I hope to run the chimney up inside the structure but may be forced to run outside if I cannot miss the structural elements of the building.

Anybody have more info or recommendations?