We are getting ready to build a masonry chimney for a 1983 defiant II, the owners manual says an eight inch flue should be used.I had the chimney block and eight inch square flue pipe delivered to my house,I noticed the flue only measured six and a half inches on the inside.Inside corner to corner it measures about eight and a half,is this acceptable.Someone told me that corner to corner is how it is measured.I plan on burning the stove with the front doors open daily for maybe an hour,I want to make sure I get good draft.The defiant II is in very good condition except for a new paint job.The mason that is building my chimney thinks i will be fine with this flue but we both want to be sure.The inside measurement of the chimney block is nine inches,I also found out that they make a eight and a half by eight and a half flue pipe.Maybe I should have got that flue instead,our main concern is building the chimney properly for this older defiant II.We are looking to get the right usage out of our stove without any problems down the road.If anyone can give us some advice it would be greatly appreciated.It would not be a problem to get the flue changed to what we need.Thank you