In order to maintain an efficient furnace, annual professional maintenance is not a suggestion—it's a requirement. AFUE will decline over the years due to ductwork leaks and inefficiencies, dirty furnace components, loose and damaged parts, and clogged air filters.
Welcome to Furnace 101, where we teach you the basics of your furnace and how it works to provide heating to your home.
The main parts of your furnace are the control system (thermostat and electrical controls), gas valve, burners, heat exchanger, blower, and duct and ventilation system. When your furnace creates heat, combustion gases are vented out of your home via a flue pipe.
The energy efficiency of your furnace is dependent on its Annual Fuel Utilization Efficiency (AFUE), which basically tells you how much of your fuel is used for heating and how much is lost due to combustion (usually out of your vents).