Disaster Resources - University of Illinois Extension

Buying Air Conditioners

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Air conditioning is a wonderful thing! It helps us enjoy summer days and provides a break from the hot, sweltering weather. But air conditioners use a significant amount of electricity, adding up to 16 percent to your annual energy bill. Choosing an air conditioner is an important decision. Buying an inefficient model will commit you to high electric bills for the life of your unit.

Types Currently Available

The type of air conditioner you need depends mostly on the climate in your area and your house size. There are three common types of air conditioners:

Room air conditioners can be mounted in windows or directly mounted in walls. Both types generally work the same way. They are sized to cool one room, so a number of them may be required for a whole house.

Central air conditioners are designed to cool the entire house. The large compressor unit is outside, and coils inside the unit cool air and distribute it throughout the house.

Heat pumps are like central air conditioners, the difference being that the cycle can be reversed and used for heating during the cold months.

Size

Most air conditioners are rated in BTU/hour (British Thermal Unit--the quantity of heat required to raise the temperature of one pound of water one degree Fahrenheit). But central air conditioning units may also list cooling capacity by tons. One ton is equal to 12,000 BTU/hour. Ask a local air conditioning dealer or energy auditor from your local utility company to come to your home and determine your cooling needs. Don't simply accept estimates by a salesperson, but do a thorough analysis to determine the proper size unit you need. With cooling systems, equipment cost is more proportional to size than with heating equipment; therefore, doubling the cooling output could nearly double the cost, so installing the proper size is crucial. When it comes to air conditioning, bigger doesn't necessarily mean better. For small homes or homes with moderate cooling loads, a window unit may be the smartest choice. Central units are almost always more efficient than room units. But the smallest unit that's adequate to cool your home is the most economical.

Efficiency

The efficiency of room air conditioners is measured by the Energy Efficiency Rating (EER). This is the ratio of the cooling output (in BTU) divided by the power consumption (in watt-hours). Look for EER ratings over 9 for room air conditioners and SEER (Seasonal Energy Efficiency Ratio) ratings over 12 for central air conditioners. The "Directory of Certified Room Air Conditioners" lists all brands and models of window units with cooling capacity and EER information. Ask a retailer for access to the store's copy.

Features And Conveniences

Energy-saving options:

  • Timers that turn the unit on and off to fit your schedule.
  • Louvers, similar to car vents, that you can close to allow other rooms to receive more air.
  • Fan-only switches allow you to use the unit for ventilation without the high cooling costs.
  • A filter check light reminds you to check and change the filter.

Air conditioners remove moisture from the air as the warm room air is forced past cold coils. Water vapor from the air condenses on the coils the same way a glass of cold water "sweats" on hot summer days. This water then drains out of the unit. You feel more comfortable and less sticky with lower humidity, but as the water vapor turns into liquid, it releases stored heat which reduces the efficiency of the air conditioner. High-efficiency air conditioners have variable speed blowers. High speed operation is more efficient, but removes less humidity in the air. Lower speeds are less efficient, but remove more moisture. If you live in a humid climate, look for air conditioner models that effectively remove moisture (pints per hour). Choose a model with a variable-speed fan to aid in dehumidifying extremely moist air.

If you live where the weather is hot for more than two or three months per year, consider central air conditioning. Where summers are dry and nights cool, a window or whole-house fan may be sufficient and much cheaper.

Buying And Installing

  • Does the system come with a warranty? What is specifically covered by it? Look for a good warranty on the compressor. Air conditioner warranties range from 1 year for complete parts and labor to 5-10 years for the compressors.
  • Make sure the business/contractor has been in business for a while and is fully bonded and insured. You'll want to know they are reliable when you need service and repairs.
  • Never place the compressor on the roof, or the east or west side of your house, unless it is shielded from the sun. Sunlight will heat the unit and reduce its efficiency.
  • Some units are noisier than others. Ask to hear one in operation before buying it.

Sources

Consumers Union. (1993). 1994 buying guide, Consumer Reports, 58(13), 318-319.

Wilson, A., & Morrill, J. (1993). Consumer guide to home energy savings. (3rd ed.) Berkeley, CA: ACEEE.

Prepared by Dawn Frankfother, Consumer & Family Economics Educator, June 1996.

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