Room Air Conditioners

Room Air Conditioners

Heating and cooling can account for more than 40% of your annual energy bill. Room air conditioners cool specific 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. They are useful when it isn't feasible to install a central air conditioning unit or when only certain rooms need cooling. Replacing a 10-year-old room air conditioner with a new ENERGY STAR qualified model can save you up to $35 on your annual energy bill.

Technology Options
Air conditioners employ the same operating principles and basic components as ae evaporator. The condenser, a hot outdoor coil, releases the collected heat outside. The evaporator and condenser coils are serpentine tubing surrounded by aluminum fins. The tubing is usually made of copper. A pump, called the compressor, moves a heat transfer fluid (or refrigerant) between the evaporator and the condenser. The pump forces the refrigerant through the circuit of tubing and fins in the coils. The liquid refrigerant evaporates in the indoor evaporator coil, pulling heat out of the indoor air and thereby cooling the home. The hot refrigerant gas is pumped outdoors into the condenser where it reverts back to a liquid, giving up its heat to the air flowing over the condenser's metal tubing and fins.

While the air conditioner cools the air, it also dehumidifies it. That's because warm air passing over the indoor evaporator coil cannot hold as much moisture as it carried at a higher temperature, before it was cooled. The extra moisture condenses on the outside of the coils and is carried away through a drain.

Room air conditioners come in "through-the-window" or "through-the-wall" models. Both can be installed permanently. Through-the-window models can be removed at the end of the cooling season when they are no longer needed.

Air conditioner efficiency has increased in the last 10 years through the use of high-efficiency compressors, fan motors and improved heat transfer surfaces.

Efficiency Ratings
Room air conditioners generally use between 5,500 Btu per hour and 14,000 Btu per hour and are less efficient than central air conditioners. Room air conditioners are rated by their energy efficiency ratio (EER), which is the cooling output divided by the power consumption. The higher the EER, the more efficient the air conditioner. National appliance standards require room air conditioners built after January 1, 1990, to have an EER of 8.0 or greater. Look for a room air conditioner with the ENERGY STAR label to maximize your energy savings.

The Association of Home Appliance Manufacturers reports that the average EER of room air conditioners increased 30% from 1980 to 1999. If you own a 1970s-vintage room air conditioner with an EER of 5 and you replace it with a new one with an EER of 10, you will cut your air conditioning energy costs in half.

The American Council for an Energy-Efficient Economy (ACEEE) publishes a guide to the most energy-efficient appliances. Visit its Room Air Conditioner page for the top rated models in various sizes.

Efficiency Benefits
The ENERGY STAR program of the EPA certifies new room air conditioners that exceed the federal minimum standard by at least 10%. ENERGY STAR qualified models must have the following minimum EERs:

Btu Rating
Energy Efficiency Ratio

Less than 8,000 Btu

8,000 to 13,999 Btu

14,000 to 19,999 Btu

20,000 Btu or greater

The following cost-effectiveness example compares air conditioning units that meet the federal minimum standard, the minimum ENERGY STAR Standard and the best available efficiency. The values are based on national averages for cooling loads with a 10,000 BTU model (lifetime 10 years) and average California electricity prices ($.12/kWh), although your actual energy use and savings use will vary with the climate you live in.

Cost-Effectiveness Example

Federal Minimum
Best Available


Annual Energy Use
765 kWh
700 kWh
640 kWh

Annual Energy Cost

Lifetime Energy Cost

Lifetime Energy
Cost Savings

Purchasing Tips

Make sure the air conditioner is the correct size. An oversized unit will lead to excessive energy consumption and poor humidity removal as a result of excessive on-off cycling. Key factors for correctly sizing a heating and cooling system include: the local climate; size, shape and orientation of the home; Insulation levels; window area, location and type; air infiltration rates; the number and ages of occupants; occupant comfort preferences; and the types and efficiencies of lights and major home appliances (which give off heat).
Insist that contractors use a correct sizing calculation before signing a contract. This service is often offered at little or no cost to homeowners by gas and electric utilities, major heating equipment manufacturers and conscientious heating and air conditioning contractors. Manual J , published by the Air Conditioning Contractors of America (ACCA), is the most common method in use in the United States. There are also many user-friendly computer software packages or worksheets that can simplify the calculation procedure.
Buy the most efficient model your budget will allow. Look for the ENERGY STAR label. Often the cost of choosing a more efficient model over less efficient one can be made up with the money you will save on your energy bill. The American Council for an Energy-Efficient Economy (ACEEE) has a list of the highest-efficiency models.
Check the yellow EnergyGuide label that must come attached conspicuously to the unit. It will allow you to compare the energy use of the model you are looking at with others in its size class.
Check the noise level of the air conditioner. A more efficient model typically will have a quieter motor and other design considerations that reduce noise indoors. Ask your retailer if you can plug the air conditioner in to see how noisy it is.