Looking for advice on Chimney

I needed to replace my wood stove the cast cracked on one side and was leaking we tried a repair but it failed. My brother had an older wood stove he was getting rid of so I took it off his hands it is bigger but was in good shape for an older stove it has the bifolding front doors with a screen and does not use fire brick.

The problem is my chimney is a Selkirk about 6 years old I have cleaned it out every year and had it inspected 2 years ago by the shop who installed it. They said it was in near perfect condition. It is 8 inch 13 feet to the cap. The issue is the new stove had an 8 inch flue pipe my brother swore it was 6 but hey for free I am not going to gripe. Can I hook the 8 inch to the 8 inch will it even draw should I try and reduce the black pipe to 6" and hook it to the 8 inch will that cause it to back up. This is not a primary heat source I have another fireplace with an osburn insert and an oil burner in the basement this is really just for enjoyment and back up heat if needed.

It would be a major job to tear out the chimney encloser to up size to a 10" chimney not to mention the cost of all the new chimney.

Thank you inadvance

An 8" stove is intended to run on an 8" chimney.

Are you sure your not measuring the outside diameter of the pipe, from the looks of the selkirk pipe a 6" flue would have around an 8" outer diameter? There is an inner and outer pipe on an insulated flue.

Ed