I would differ with the "without a doubt" part. With his gas rate of $1.20/therm, even a high (90%) efficiency gas furnace only produces 75K BTU's per dollar.
Originally posted by irishmist
I would strongly suggest you look into a "dual-fuel" system. This utilizes a combination of heat pump and fossil fuel, in your case natural gas. I am just up the road from you in Ohio Valley, and I have lived in heat pump, natural gas, and now dual-homes, and without a doubt this is the best arrangement. It allows the heat pump to satisfy the heating requirement during those temps when it is most efficient (more than gas) and then lets the gas kick in when it is most efficient (more than electric) without any sacrifice in comfort (which was a real important consideration for me)