Comparing Air Conditioner Efficiencies

Air conditioner units are rated for efficiency and size to help homeowners determine which one is best for their needs. Purchasing a unit that is too large, too small or barely meets minimum national energy-efficiency requirements will result in higher energy bills over time. In some instances, spending more on the unit will save you money on your energy bills every month. Those savings add up quickly.

Location
The position of your home geographically as well as the room where the air conditioner is installed are both major factors in how efficient your air conditioner will be. If your home, or the room, is well shaded, the air conditioner will need less energy to cool the area. Likewise, rooms on sunny sides of the house will require more energy to cool. Rooms with multiple windows or doors tend to lose more air and affect the efficiency of individual room air conditioners. Select a higher rated air conditioner for harder to cool areas and a lower rated air conditioner for less heated rooms.

Size and Ton Rating
Air conditioners both cool warm air and remove humidity. Purchasing an air conditioner that is too large for the room will cool the room faster but not remove as much humidity, making the room feel warmer than it is. This is called short cycling and it reduces the efficiency of the air conditioner. In contrast, a unit that is too small will need to run longer to cool the room, which also reduces efficiency. The size of the air conditioner is rated in tons per kilowatt. This rating refers to how many British Thermal Units (BTU) the unit outputs with one ton equal to 12,000 BTU. A 250 to 300 square foot room needs approximately 7000 BTU for efficient cooling.

Star Rating
Energy Star rates air conditioners between one and five stars. The rating is only given to products that have proven to reduce energy substantially. For more expensive air conditioner models, the Energy Star logo and rating is only awarded if the consumer will save the same or more than the monetary difference in cost over less expensive comparable models. Another factor in determining Energy Star compliance is the energy efficiency rating (EER). An air conditioner must be rated 14 or higher to earn the Energy Star logo.

Energy Efficiency Rating
The Energy Efficiency Rating is a measurement of how well the unit cools when the temperature outdoors is at a specific temperature. EER is used on room sized air conditioners and on central air conditioners it is referred to as the Seasonal Energy Efficiency Rating (SEER). The rating is determined by dividing the number of BTU the unit outputs by the total energy input in watt-hours leaving a simplified and smaller number. This number is the rating and it is similar to the miles per gallon rating on automobiles. The number is beneficial in determining the cost of operating the air conditioner unit. The higher the EER or SEER rating, the more efficient the air conditioning unit.