The heat pump uses a reverse air conditioning cycle to deliver heat. The refrigerant, or freon as you may call it, is compressed, and sent to the inside coils where it gives up it’s heat to the inside air, and returns to the outside coils where, hopefully, the refrigerant will become a gas a again, to be re-compressed, and returned to the inside coils. If the refrigerant does not become a gas soon enough, it can damage, or destroy the compressor. To this end, extra heating coils are used to prevent this, making the heat pump, in colder climates, less efficient. An air conditioning unit is just an air conditioner. It compresses the refrigerant, which goes through the outside coils to become a liquid, goes inside to the indoor coils where it picks up heat by turning into a gas again, and returns to the compressor to begin the cycle again. Your best choice, prices of fuel not with standing, is to use a gas furnace, and a regular air conditioner for your central air conditioning system. Gas, is a better heating fuel, than a heat pump, or resistance wire heating system.