Heat pumps are an energy efficient system used to provide air conditioning in the summer and heat to your home in the winter. In simple terms, a heat pump is an air conditioner in the summer time and a heater in the winter. It takes the heat from the house and expels it outside. In the winter, it extracts heat from outside air and circulates it inside the house. If the weather gets very cold, then a supplemental heat source (i.e. a gas furnace) kicks in to add additional heat.