When it comes to air conditioners, proper sizing, selection, installation, maintenance, and correct use are keys to cost-effective operation and lower cooling costs.

Types of Air Conditioners

The basic types of air conditioners are room air conditioners and central air conditioners.

Room Air Conditioners

Room air conditioners cool rooms rather than the entire home. If they provide cooling only where they're needed, room air conditioners are less expensive to operate than central units, even though their efficiency is generally lower than that of central air conditioners.

Smaller room air conditioners (i.e., those drawing less than 7.5 amps of electricity) can be plugged into any 15- or 20-amp, 115-volt household circuit that is not shared with any other major appliances. Larger room air conditioners (i.e., those drawing more than 7.5 amps) need their own dedicated 115-volt circuit. The largest models require a dedicated 230-volt circuit.

Central Air Conditioners

Central air conditioners circulate cool air through a system of supply and return ducts. Supply ducts and registers (i.e., openings in the walls, floors, or ceilings covered by grills) carry cooled air from the air conditioner to the home. This cooled air becomes warmer as it circulates through the home; then it flows back to the central air conditioner through return ducts and registers. A central air conditioner is either a split-system unit or a packaged unit.

Buying a New Air Conditioner

Today's best air conditioners use 30% to 50% less energy to produce the same amount of cooling as air conditioners made in the mid 1970s. Even if your air conditioner is only 10 years old, you may save 20% to 40% of your cooling energy costs by replacing it with a newer, more efficient model.

Proper Sizing

A larger-than-needed air conditioner will not provide the best cooling. In fact, running a smaller unit for a longer time will use less energy to completely condition a room than running a larger unit for a shorter time. Buying an oversized air conditioner is a bad idea for the following reasons:

• It costs more to buy a larger air conditioner than is needed.
• The larger-than-needed air conditioner cycles on and off more frequently, reducing its efficiency. Frequent cycling makes indoor temperatures fluctuate more and results in a less comfortable environment.
• Frequent cycling also inhibits moisture removal. On humid days, removing moisture is essential for acceptable levels of comfort.
• The more frequent cycling also wears out the compressor and electrical parts more rapidly.
• A larger-than-needed air conditioner uses more electricity and therefore costs more to operate.

For the installation of a central air conditioner, your contractor should use industry approved standards for calculating the size of the new unit. The U.S. Department of Energy Web site provides consumers with information about the methods used in making these calculations.

Sizing Guidelines for Room Air Conditioners

To determine the proper size of a new room air conditioner, calculate the square footage of the area to be cooled by multiplying the length of the room in feet by the width of the room in feet. Using the chart below, match the size of the area to be cooled with the air conditioner capacity that's right for your situation.

Installation

• Install your air conditioner on the north, east or best-shaded side of your house.
• Make sure the window area around your air conditioner is properly sealed to reduce cold air loss.
• Insulate the attic or building envelope of your house to reduce cooling and heating costs.
• Inspect your attic ventilation to make sure that soffit, ridge or gable vents are unobstructed and can remove excess heat and moisture in your attic.

Operation

• Set the thermostat on your central air conditioner at the highest temperature consistent with your comfort and health requirements.
• Install a timer or clock thermostat on your air conditioner. Program your unit to run just before you arrive home rather than having it run all day.
• Delay cooking, baking and other activities that produce heat and humidity until the cooler times of the day or night.
• Use a portable or ceiling fan to circulate the pre-cooled air in your air-conditioned home.
• In very humid weather, adjust your cooling system's fan speed to a low setting.
• As the sun moves from east to west, pull draperies and shades on windows to block out the heat.
• Avoid cooling rooms that aren't used or occupied.
• Keep shrubbery away from your air conditioner since blocked vents reduce your unit's ability to exhaust air.
• Move furniture, plants and draperies away from the front grille intake section and top air discharge section of your window air conditioner.
• Don't run your unit when the outdoor temperature is below 70 degrees. You'll not only waste money, you'll also run the risk of causing premature compressor failure.

Maintenance

• Have a qualified technician service your air conditioner annually and have the following checked: proper refrigerant charging, condenser coils, evaporator, fan blades, fan motors and filter.
• Check, clean or replace the filter in your air conditioner at least once a month.
• Reduce cold air loss to a minimum by insulating or sealing leaky cooling ducts.