Definition
Annual Fuel Utilization Efficiency (AFUE) measures what share of the fuel a furnace burns actually becomes usable heat in your home over a year. A 95% AFUE furnace converts 95 cents of every fuel dollar into heat and sends the rest up the flue. In a heating-dominant climate like West Michigan, AFUE has a direct, season-long effect on your gas bill.
Why this matters for your home
Older Grand Rapids furnaces often run at 80% AFUE or lower, while modern high-efficiency units reach 95–98%. The higher the AFUE, the less you pay to stay warm through a long Michigan winter — which is why AFUE is one of the first numbers to compare when replacing a furnace.