The Energy Efficiency of a Window Air Conditioner vs. a Vertical Air Conditioner

Windows Units

• In general, window unit air conditioners tend to be less efficient than central air conditioners, but this depends somewhat on the individual cooling needs in your home. If only one or a few rooms in your home require air conditioning, installing and using two or three window units will be more cost efficient than using a central air conditioner that will cool parts of the home you do not need to have cooled. Room air conditioners also typically require less electricity than central air conditioners; most smaller window unit air conditioners can be plugged into a standard 115-volt home electrical outlet that does not share a circuit with any other major appliances.

Central Air Conditioning

• If your entire home needs to be cooled with air conditioned air, then central air conditioning is almost always a more energy-efficient option. As is usually the case with major home appliances, though, the age and mechanical condition of the central air conditioner will determine, in large part, its energy efficiency. Old outdoor compressors for central air conditioners, for example, tend to be much less energy efficient than newer models. The condition of the duct work in your home that circulates air conditioned air also plays a role; leaky duct work means more air-conditioned air will be lost before it is able to cool your home.

Calculating Efficiency

• To put a specific number to the energy efficiency of each of these appliances, look at the product's labeling when you purchase a new unit. A room air conditioner's energy efficiency is measured in terms of energy efficiency ratio whereas a central air conditioner's efficiency is measured in terms of seasonal energy efficiency ratio. For both of these metrics, the higher the number, the better. Federal regulations require air conditioner manufacturers to place both ratings prominently on new air conditioners, so always shop for air conditioners with the highest EER or SEER ratings in order to maximize energy efficiency.

Other Considerations

• Whether you use a room air conditioner or a central air conditioner, the manner in which you use these devices plays a major role in how efficient or inefficient they are. Use natural ventilation such as open windows and ceiling fans as much as possible to minimize your reliance on air conditioning to keep your home comfortable. Set the thermostat at as high a temperature as possible while still maintaining a comfortable temperature in the home. Use a programmable thermostat to set the air conditioner at a higher temperature when no one is in the home in order to increase energy efficiency further.