Guess I answered my own question. Had a chimney sweep do an inspection. Flue looked fine but he said I definitely need a liner. He doesn't install/sell them so it isn't in his interest to give me a bogus answer. Posting on http://chimneysweeponline.com/holinst.htm
indicates "Code prohibits venting any woodburner into a chimney flue with a cross-sectional area (CSA) that is more than three times the CSA of the flue collar on the stove. Thus, if your stove has a 6" flue collar (28 sq.in. CSA), the chimney flue must have a CSA less than 84" (3 x 28). "