When purchasing new air conditioning equipment, be sure to check the efficiency rating of the proposed unit. A higher-efficiency rating will result in lower operating costs. Cooling energy efficiency is designated by the term ""SEER"" (Seasonal Energy Efficiency Ratio) for residential central air conditioning systems (5 tons or less). Window air conditioners are rated using "" EER"" (Energy Efficiency Ratio), as their use is typically intermittent. Both of these terms are a measure of the unit's output or cooling capacity compared to the power consumption at standard conditions. New units have EER's/SEER's ranging from 10.0 to as high as 17.0.

For split systems with an outdoor unit and an indoor coil, the efficiency is affected by the match between the indoor cooling coil and outdoor condensing unit. The manufacturer’s product data should be consulted to determine the combined efficiency. The American Refrigeration Institute (ARI) publishes an annual directory listing various combinations of outdoor units and indoor coils with their SEER or EER rating. Most major manufacturers' product lines are included in this directory.

Besides a unit's EER or SEER, there are additional energy-saving features to look for when selecting an air conditioner for your home.

Correct system sizing is critical to ensure optimum efficiency. Both over- and under-sizing can lead to poor operating efficiency. The size of the unit is a function of the compressor, the main energy-consuming component. The larger the compressor the more energy will be required to operate the system. An oversized unit will cycle (turn on and off) more frequently. Frequent cycling prevents the air conditioner from adequately dehumidifying the air. Both dehumidification and cooling are necessary for an air conditioner to provide comfortable indoor conditions during hot, humid weather. An undersized unit will operate longer and may not have the capacity to adequately cool the house to the desired temperature. When it is time to replace your current air conditioning system, have the air conditioning contractor perform a load calculation to determine the proper size unit.

General maintenance of your air conditioning equipment is simple and will keep the unit working at optimal performance. The following guidelines should be followed to get the most out of your system.

• Keep the manufacturer's instructions, control drawings, design documents, and any other relevant information for future reference.
• Maintain adequate space around the outdoor unit to avoid restricting airflow across the coils.
• Keep the outdoor condensing unit shaded from the summer sun.
• Replace filters regularly. Vacuum dirt and dust from
the indoor coil once a year to prevent restricted airflow.