AFUE stands for Annual Fuel Usage Efficiency. The AFUE shows how efficiently a furnace transfers heat from the energy created by burning the gas to the house. The higher the AFUE rating the more energy-efficient the furnace. The mandatory minimum AFUE rating in Canada is 90 percent.
The top of the line Signature (SLP98) furnaces have 98% efficiency! Most of the Elite (EL) furnaces have 96% efficiency.