We did the same thing in our raised ranch. We had a central a/c unit at the end of its life and decided to go with the heat pump instead of replacing it. We had to put in a mini split downstairs because our duct work was only on the upper level. With the way oil prices are now, we will definitely save money this winter. FYI if you go with a Carrier heat pump they have a 3-year 0% financing payment option.