When you see that a furnace has an AFUE rating of 95 or 98 that tells you how much heat is delivered in a single heating season.  AFUE stands for Annual Fuel Utilization Efficiency.   A rating of 95 means that 95% of the energy put into the furnace is used to heat your home and the other 5% is put out through the flue.  So of course the the higher the AFUE the more efficient the furnace is.