One indicator is Annual Fuel Utilization Efficiency (AFUE). All heating equipment manufactured after 1980 is required to have a label indicating its AFUE. The AFUE ratio is a measurement of a heating system’s seasonal efficiency, taking into account how well the system performs over an entire season of starts and stops. Modern heating systems can range in efficiency from 81% to 95%. If your system’s AFUE is lower than this range, we recommend that you contact us to talk about your replacement options.