What Is the Energy Cost for a Window Air Conditioner?

Room Air Conditioners

• A measure of an air conditioner's efficiency, the energy efficiency ratio, or EER, represents the ratio of the cooling capacity to the watts or power input. The more efficient air conditioners have a higher EER number. When you shop for a new air conditioner, look for an EER of 10 or above. The federal minimum EER is 8 to 9.8. The energy efficiency of air conditioners has increased since the 1970s, so you might find it worthwhile to replace that old room unit from the 1970s or '80s.

Comparison

• The average window air conditioner uses approximately 134 kWh/month. In comparison, a ceiling fan uses 85 kWh/month. A 24-inch box fan uses even less, at 30.6 kWh/month. Central air, at 12,000 BTU per hour, uses 1.2 kWh/hour at 10 EER. Moving up to the more efficient 14 EER would cause the energy use to drop to .85 kWh/hour. Multiply kWh/hr by the number of hours used in a month to get the kWh per month comparison. Although the efficiency of a room unit is lower than that of central air, the central air uses more energy.

Size

• Air conditioners are sized in British Thermal Units, or BTUs. Window units range from 5,500 BTUs per hour to 14,000 BTUs per hour. A small unit that runs continuously is more efficient than a large unit that constantly cycles on and off. In general, figure about 20 BTU for each square foot of space you want to cool. Most household electrical receptacles rate 115 volts. Some large window air conditioners need a 230-volt circuit, which would require special wiring.

Considerations

• No matter what size your window air conditioner, you can reduce its energy use. Try to install the unit where direct sunlight won't hit it. Keep the unit away from lamps or televisions, as the sensor will register heat from these appliances and run longer. When the humidity is high, set the fan on "Low." This will cause the air to move more slowly through the unit, thus removing moisture from the air more efficiently.