The AFUE number is about fuel, not comfort
The efficiency rating on a furnace's label tells you how much of the fuel it burns actually turns into heat for the house, versus what goes out the vent. A higher rated furnace pulls more heat out of the same flame. It doesn't tell you how fast the house warms up or how evenly, and it isn't a measure of the furnace's output. A smaller furnace with a high rating can still be the wrong size for a given house.







