Auxiliary heat means that the unit uses a supplemental system to generate the heat that is required by the homeowner or the house. Generally, you will be able to notice a sign in your thermostat that auxiliary heat is being used by the system. Here it must be noted that the heat pump process is effective when the outside temperature is anything between 25 and 30 degrees Fahrenheit. When the temperature falls below that level, the system uses supplemental heat to keep the house warm. The heat in this case is provided by an alternate source such as the gas furnace or electric heat. If the source of heat is the gas furnace, the heat pump turns off and if the source is electric heat then it works along with the heat pump. Auxiliary heat is greatly helpful even when the heat pump malfunctions.