Most systems have a lifetime of 10 to 20 years. As your equipment gets older, its efficiency can decrease dramatically. You may notice that it gets noisier and needs repairs more often. When a unit begins to show its age, you have two choices: overhaul the system or replace it. Because heating and air conditioning technology improves over time, a unit designed with newer, more energy-efficient equipment makes sense, especially if your system is 10 or more years old.