Air conditioning systems are typically rated based on their cooling capacity, energy efficiency, and other performance characteristics. The cooling capacity of an air conditioning system is typically expressed in terms of British thermal units per hour (BTUs/hr) or tons. One ton of cooling capacity is equal to the amount of heat that can be removed from a building or a space in one hour by an air conditioning system with a cooling capacity of 12,000 BTUs/hr. The size of an air conditioning system is typically based on the cooling needs of the building or space it is designed to serve, and it is important to properly size the system to ensure that it meets the cooling needs of the building or space and operates efficiently.

Energy efficiency is another important factor in the rating of air conditioning systems. The energy efficiency of an air conditioning system is typically expressed in terms of its energy efficiency ratio (EER) or its seasonal energy efficiency ratio (SEER). The EER is a measure of the efficiency of an air conditioning system under standard laboratory conditions, while the SEER is a measure of the efficiency of the system over an entire cooling season. Higher EER and SEER ratings generally indicate a more efficient air conditioning system, which can result in lower energy costs and reduced greenhouse gas emissions.

Other performance characteristics that may be considered in the rating of air conditioning systems include the noise level of the system, the durability and reliability of the system, and the availability of features such as zoning, programmable thermostats, and air filtration. In addition to these factors, the type of system (such as a split system, a packaged system, or a ductless system) and the size and layout of the building or space it is serving can also be important considerations when selecting and rating an air conditioning system.