Annual Fuel Utilization Efficiency (AFUE) is a measure used to evaluate the efficiency of heating systems, particularly furnaces and boilers. It represents the percentage of fuel that is converted into usable heat over a year. For example, an AFUE rating of 90% means that 90% of the fuel consumed is used for heating, while the remaining 10% is lost. AFUE ratings help consumers compare the efficiency of different heating systems. Higher AFUE values indicate more efficient systems, which can lead to lower energy bills and reduced environmental impact. Understanding AFUE can assist homeowners in making informed decisions about their heating options.