We live in a small 2BR house, that has an oil-fired Energy Star baseboard hot water heating system. Three years ago, we did a DIY install of an 18,000 BTU ducted "ductless" heat pump system, which uses the ductless compressor and stuff in a small air handler. Dropped our summer electric bills by over half compared to two window AC units, and trimmed 25% off of our heat costs in the winter.
The heat pump is rated for -4F at the low end, but in reality it starts struggling below 15F in our setup. We wind up running the oil system for 1-2 weeks every winter because we have it, to handle upstate NY's cold snaps. The heat pump and a few electric heaters would probably do us fine if we didn't have the oil system for heat (and use it for hot water as well).
With that said, the ducted "ductless" costs twice what a traditional ductless system does. We didn't have the wall space for a ductless air handler in any room. There are the usual wall-mounted air handlers, as well as floor-mounted ones, recessed ceiling units, and the ducted "ductless" that we used:
A ducted "ductless" system, concealed in ceiling headers:
The plans for our SC Garage Mahal call for using ductless and multiple compressors throughout for redundancy in case one fails. SC does not see the winter lows of NY, but does get a bit warmer in the summer. From experience with the current system, I'm going to upsize one level over the recommended size for each unit just to have the reserve capacity.....