Whats the difference between mid-efficiency and high-efficiency gas furnaces?
The efficiency ratings of furnaces is measured in AFUE as a percentage. AFUE stands for Annual Fuel Utilization Efficiency, and it’s what furnace manufacturers use to inform us of the efficiency of their equipment. Standard efficiency gas furnaces have efficiency rating of 60% to 70%. Mid-efficiency gas furnaces have an AFUE rating of around 80%. High-efficiency gas furnaces (aka condensing gas furnaces) have efficiency ratings in excess of 90%. To visualize what the percentage means, deduct the efficiency from 100%. whatever you have left is what the furnace doesn’t use. Thus, for an 80% efficient gas furnace, 20% of the gas you purchase is going up the chimney. For a 93% efficient (high-efficiency) gas furnace, only 7% of the gas purchased is going up the chimney.
