The EFM DF-520 is a great oil/coal boiler. Its good for oil and even better for coal. The price varies depending on the dealer so call around for the best price. You can get a list of dealers in PA from the EFM site:http://www.efmheating.com/dealers.html
The DF-520 does not offer automatic switch over, but its simple to do if the coal fire goes out for whatever reason. I am sure your wife can do it. I travel occassionally, and want my wife to switch it over to oil if needed. Hopefully, I can get her to empty the ashes while I am gone to stay on coal. With all the money saved on burning coal instead of oil she might be able to go buy some clothes as an incentive to help empty the ashes!