[Starchy]

I have an elderly friend who just bought a cottage with an old airtight wood stove. This stove has an 8" flue, with double wall black pipe to the 8" stainless Selkirk metalbestos chimney. I believe the chimney is about 25 years old, but looks to be clean and in good shape. The stove burns well as she has had several fires and it seems to work well. The problem is that the wood stove is not certified by either UL or CSA, and the insurance company has said that it must be replaced with a new, certified stove. No problem except that all new stoves seem to be 6" flue, and the existing chimney is 8". Can a liner be added to the chimney to make it 6" or must the chimney be replaced as well?
Thanks for any input.