I have a 20 y/o vermont casting winter warm insert in need of replacement. It has a 8 inch vent to a fully lined chimney. I have looked at pacific energy summit insert,hearthstone and others that use a 6 inch vent. The cost of replacing the lining is alot. I have found a Lennox Hearth insert that uses 8 inch. Can I simply install that and save the expense of a new liner? I've been told by one installer that due to code (i am in maryland) the lining should be replaced. Any thoughts?? thanks,kjb