The heat pump is an air conditioner that reverses the process of removing heat from the inside of the house in summer to absorbing the heat from outside air and moving it inside in winter. It is effective by itself down to temperatures around 25 to 30 degrees Fahrenheit. At that point, either a gas furnace or an air handler with supplemental electric heat will kick in and help heat your home. The Auxiliary Heat light on your thermostat will light. The heat pump will continue to operate along with the electric auxiliary heat. It will shut off when a gas furnace is energized. Emergency heat is a manual override option in the event your heat pump needs service.