The amount of energy used to air condition a building depends on the size and layout of the building and the air conditioner's seasonal energy efficiency rating. A licensed heating and air conditioning contractor can estimate how much energy a given system uses to cool a given building.
The seasonal energy efficiency rating number, or SEER, measures an air conditioner's efficiency. The SEER number is the ratio between the amount of heat the air conditioner can remove in one hour, as measured in British thermal units, and the amount of energy the air conditioner consumes while removing that heat, as measured in kilowatt-hours. The higher the SEER, the more efficient the air conditioner. Other factors that can affect the amount of energy consumed are the building's insulation and layout, the use of window coverings to block sunlight, and the use of programmable thermostats to ensure that the system runs only as needed.