If you’re comparing the cost of operating a new heating system for your home, you may find yourself wondering “What is AFUE?” Short for Annual Fuel Utilization Efficiency, AFUE is the metric utilized to express the efficiency of a gas furnace which, in turn, is one of the major factors that predicts monthly heating costs.

What Is AFUE Percentage All About?

The AFUE rating indicates the percentage of gas combustion that actually warms your home vs. the amount of heat lost in the combustion process, usually exhausted through the furnace vent. The federal minimum AFUE for standard, efficiency gas furnaces is 78%. This means 78% of the heat generated by gas combustion warms the house while 22% of that heat is lost through hot gases released up the vent. 

So what is the AFUE percentage in high-efficiency furnaces? These efficient units start at 90% efficiency and today range as high as 98.7%. By utilizing a process to extract extra heat from condensation in combustion gases, heat loss in high-efficiency units is reduced to just 10% and ranges down as low as 1.3%. Substantial monthly savings result, as less gas is consumed to produce more heat than standard furnaces. 

The question “What is AFUE?” raises additional issues to consider when choosing between a standard efficiency furnace and a high-efficiency model.

  • Monthly operating costs of a standard AFUE 78% furnace will be higher than the 90% higher-efficiency AFUE unit. However, the upfront purchase price of the standard unit will be considerably lower than the AFUE 90% model. 
  • AFUE 90% furnaces require specific installation alterations, including PVC piping to properly discharge the liquid condensate produced during heat extraction. In addition, these high-efficiency units require a separate fresh-air intake pipe and warm-air exhaust pipe, which are routed laterally through an exterior wall, vs. the vertical exhaust pipe of a standard furnace that extends upward through the roof. 

For more answers to furnace efficiency questions like “What is AFUE?”, contact the pros at Mowery Heating, Cooling and Plumbing.