If your system is 10 years and older, you should consider replacing your system because it may be costing 40-60% more in energy costs each month. System 10 years ago were not as efficient as systems today. Most systems 10 years ago were under 6-10 SEER systems. Day and Night air conditioner or heat pump systems are up to 19 SEER which means they are nearly twice as efficient as your old system. Also, consider replacing your system if you are experiencing frequent repairs, hot or cold spots in your home, or a noisy system.