If you have a central air conditioning system or a heat pump that's over ten years old, a question you may be asking yourself is this: "Is it better to let the system wear out completely before replacing it, or to replace it at some point before it wears out?"

According to the Trane Home Comfort Institute, a consumer information service on heating and cooling, you'll probably save money by replacing your old system before it wears out. That's because today's generation of central air conditioning systems and heat pumps are so much more energy efficient than their older counterparts.

The efficiency of a central air conditioner is indicated by its Seasonal Energy Efficiency Ratio or SEER. The higher the SEER, the more efficient the unit. The more efficient the unit, the less electricity needed to operate it.

In recent years, manufacturers of air conditioners and heat pumps have made dramatic progress in increasing the SEER of their units. As a result, it may make economic sense to purchase a new, more efficient unit now and immediately lower your operating costs.

Eventually, the more efficient unit will pay for itself through decreased utility bills. In the meantime, you'll gain the added benefits of greater reliability and longer warranty protection.

Another benefit of a higher efficiency unit is a lower life cycle cost, which is the total of the operating and maintenance costs over the life of the system.

Trane Home Comfort Institute experts explain that a system with a higher SEER may have a higher purchase price than one with a lower SEER. However, because of its higher efficiency, it will use less energy to cool your house, resulting in lower electric bills. In many cases, these savings are more than enough to offset the additional cost of the higher SEER unit.