My father's house was built in 1928 with a 25 foot, brick chimney and NO lining. It was heated with coal for about 45 years and oil for the past 35 years. The chimney is still intact, but the mortar joints are now soft near the top.
There are at least two grades of stainless for a liner; 304 and 316. 316 is meant for coal.
My bother-in-law is getting a Hitzer 983 insert installed by the dealer in two weeks. He told him that if his chimney is in good shape which it is (only 10 years old) that you don't need a liner. They just take the damper out and push the insert in, then pack it all in real tight with insulation. I was thinking they would put a 6 ft peace up past the damper but the guy said theres no need for it. I'm gonna watch them do it then i'll know for sure how it's done.