@Oldfartrant when we moved in and were looking at replacing our oil furnace we were going to have to increase the size of the duct work which was going to be a massive cost. There were no mini-split type heat pumps then (2005) so we just went to electric baseboard. Then we went to mini splits a few years back. One unit on the outside, two inside, one for the main and one for basement floors. It was still less ($15K in 2018) than the ducting option. If we want to do the top floor we would need a 2nd outside unit and two more indoor but we are good for now