A Heat Pump is a reverse cycle air conditioner. When you run your air conditioner, your outdoor unit will be blowing hot air,( in other words removing the heat from your home and sending it outside). When you run your heat, you reverse the flow of refrigerant and remove the heat from the atmosphere outside and blow it inside. When the temperature dips below 40 degrees outside, the Heat Pump labors in producing heat so they install a back up or auxiliary electric heat strip to supplement the Heat Pump. Electric Heat strips are very expensive to operate. In southern climates where it rarely dips below 40 degrees the heat pump is very efficient. A 3 to 1 savings in heating compared to electric heat strips.