Currently I am receiving quotes on replacing my gravity furnace and installing a new gas furnace with a/c. Unfortunately I can't seem to get two contractors to recomend anything remotely similar. The house is a 2-story and 80 years old. It has no insulation in the walls. The duct work is original. I am in Mid Ohio so the winters can be mild or brutal as well as the summers. The house is gennerally much cooler than outside since it is a wooded area. How efficient of a heating system would I need? Is it worth the extra cost to get a 90% efficient system. Please forward any comments to my email address. Thank you for your help.