AFUE stands for Annual Fuel Utilization Efficiency. This ratio measures how much fuel converts into usable heat and indicates if a furnace is energy efficient. So, a furnace with a 95 percent AFUE rating will turn 95 percent of the fuel into heat. This means furnaces with a 95 percent AFUE rating operate more efficiently than furnaces with an 80 percent AFUE ratio. Energy Star qualified furnaces feature a high AFUE rating.
When comparing the efficiency and operating cost of two furnaces, take into consideration the type of fuel they use to operate. Electric resistance furnaces operate with 100 percent efficiency in that all incoming electricity converts to heat. However, while these seem like high efficiency furnaces, the cost of electricity remains higher than natural gas or propane.
CFM stands for Cubic Feet per Minute. It measures the volume of air that a fan moves. The higher that number, the more air it can move.