AFUE ratings are one way to compare the efficiency in furnaces.
Many years ago, the Federal Trade Commission started to require that all heaters have AFUE ratings.
The AFUE rating is how much heat a furnace will produce compared to the amount of fuel that it loses. If a furnace has an AFUE rating of 90%, then that means that 90% of all energy created by the furnace gets transmitted to the home. 80% furnaces aren’t very energy efficient, but they are cheaper. Some of the most efficient furnaces on the market are often 98 or 99% effective. In very cold climates, it’s important to choose a high-efficiency furnace that has an AFUE rating higher than 90%. If the weather in your area is mild, then you can probably get away with something less effective and cheaper. If cold climate, snow, and ice are regular winter worries, then choose a gas furnace that can work efficiently on the hardest winter days. My wife and I picked up a very nice multi furnace with a 98% off you rating to use in our home. The temperatures in this area are always below freezing during the month of January, February, and March, and winter can last a long time. We chose a furnace with a high energy efficiency so we never have to worry about heating the house during the winter season. Even though it was costly, the choice was easy to make with three kids, a dog, and 2 cats in the house. The health and well being of our family has to be the first thought on our mind.