Have annual preventative maintenance performed on your system to make sure your system is performing at its peak efficiency or upgrade to a high efficiency system and Install programmable thermostats
Most systems have a life expectancy of 15 to 20 years. As your equipment ages its efficiency can decrease dramatically.
In this case, bigger is not always better. The system that is best is the system that is sized to the house. Air conditioners control the comfort level by cooling the air and removing the humidity. An over-sized air conditioner can cool your house faster using more energy and it will not remove humidity adequately. In addition, if you have existing ductwork it may not be sized to support the air flow of a larger system. A unit that is too large for your home will have a short run cycle. It may take a short time to cool the air but the unit will shut down before enough air blows across the indoor coil where moisture condenses into water and drains from your system. Too much moisture left in the air can lead to mold and mildew problems. These short cycles also mean your system has to start and stop more often which will use more energy and increase wear and tear on your system. An air conditioner will operate more efficiently during run cycles.
As a rule of thumb, it pays to replace your existing home system when the cost of repairs reaches 30% of the price of a new purchase or when utility bills have increased by 50%. Learn how replacing your system can actually pay you back.