When choosing clothing, one size sometimes fits all. Unfortunately, that's not the case when choosing a central air conditioning system for your home.

Choose a unit that's too large, and it will cost more to purchase, more to operate and probably won't remove enough humidity from the air to make you feel comfortable. Choose a unit that's too small, and it will lack the capacity to give you the comfort you want on the hottest days. The best choice is a system that's just the right capacity for your home.

Experts at the Trane Home Comfort Institute explain that if an air conditioner has too much capacity for your home, the air will cool quickly, but you may not feel comfortable because the unit will not run long enough to remove the humidity. That's because moisture is removed as air is drawn across the cooling coil.

Another disadvantage of an oversized central air conditioner is higher electric bills caused by the constant stopping and starting of the unit. A properly sized unit can actually run for longer periods of time with a lower energy consumption than a unit that's too large. Short operating cycles can also shorten the life of the equipment.

On the other hand, a unit that's too small for your house may never get the job done on a hot day, even if it runs nonstop. For example, if you set the thermostat at 76 degrees on an extremely hot day, an undersized air conditioner may only be able to reduce the temperature to 80 degrees.

Selecting the right size air conditioner requires more than a rule-of-thumb square-footage estimate, a telephone conversation with a dealer or a quick look around the house.

According to Trane Home Comfort Institute experts, the best way to make sure you're getting the right size unit is to have an independent air conditioning dealer come in and give your house a thorough inspection.

A skilled dealer can usually obtain the information needed to complete a cooling load analysis in an hour or two, after which he'll be able to accurately determine the size of the system your home requires for a comfortable temperature and humidity level.