AFUE (Annual Fuel Utilization Efficiency)
Definition: A measurement of the seasonal energy efficiency of gas heating equipment. It is the annual output energy of the equipment divided by its annual input energy, expressed in consistent units (i.e. Btu-out per Btu-in). Thus, the resultant value of AFUE is unit less. AFUE includes any input energy required by the pilot light but does not include any electrical energy for fans or pumps.