What are furnace ratings?
Furnaces are rated by the Annual Fuel Utilization Efficiency ratio (AFUE), which is the percent of heat produced for every dollar of fuel consumed. Like the miles per gallon on your car, the higher the AFUE rating, the lower your fuel costs. All furnaces manufactured must meet at least 80% AFUE. If your furnace is 10 to 15 years old, it probably falls well below the current furnace minimum and wastes energy.