I'm curious as to how low a temperature your heat pump will operate. I live in New England and replaced a whole-house air conditioner with a heat pump, but the heat pump works only to 35F. Much colder than that, and an auxiliary electric heater kicked in. The first Winter cost me about $800 over my gas-fired forced hot water heating system. I had the contractor disable the electric heat in the Spring and rewire the thermostats to start the (high efficiency) furnace when the outdoor temp got too low.