Answer:
Air conditioners are rated by the number of British Thermal Units (BTU) of heat they can remove per hour. Another common rating term for air conditioning size is the "ton," which is 12,000 BTU per hour.
Each air conditioner has an energy-efficiency rating that lists how many BTUs per hour are removed or “pulled out” for each watt of power it draws.
The efficiency rating for room conditioners is the Energy Efficiency Ratio, or EER.
The efficiency rating for central air conditioners, is the Seasonal Energy Efficiency Ratio, or SEER.
These ratings are posted on an Energy Guide Label, which must be conspicuously attached to all new air conditioners. Energy Star-labeled appliances mean that they have high EER and SEER ratings