Air Conditioning contractors calculate how much cooling a home needs according to the guidelines set forth in the Manual J of the Air Conditioner Contractors of America (ACCA).

The following guidelines are used to maximize the long investment in your home cooling system:

• Buy a high-efficiency unit. New air conditioners are required by federal law to have a SEER of 13 or higher. Even though it will cost more, it's usually worth it to buy at least a SEER 14 unit, because over time that initial investment will be paid back with energy savings. Look for an ENERGY STAR label when you shop. If you are replacing an existing air conditioner, you must replace the whole unit, including the inside coil and often the blower fan, to achieve the rated efficiency.
• Install for ease of maintenance. Make sure the inside coil can be reached for cleaning. The contractor may have to install an access panel, depending on the model. The coil should be cleaned every two years. The air filter should be located where it is easy to remove. Check it every month during the summer, and clean it or change it whenever it is dirty.
• Place the outside unit on the north or east side of the house, out of direct sunlight, but don't add shade for it. Leave plenty of room for free air flow on all sides, and leave at least 4 feet of clearance at the top. Keep the area free of debris and shrubbery. The air conditioner draws a lot of air through it. It's more important for the unit to have a lot of space than for it to be well shaded.
• Another important consideration is the ability of the selected air conditioner to remove moisture from the air. Different models have different abilities to handle moisture. The contractor should understand how to pick an air conditioner that is suitable for your house, and for your climate. For more on choosing the best unit for your needs, and on dealing with contractors, see above.