Air conditioning is a common feature in many homes in the United States, with approximately three-quarters of all homes being equipped with an air conditioner. These systems use a significant amount of electricity, accounting for about 6% of all electricity usage in the country and resulting in annual energy costs of about $29 billion for homeowners. The use of air conditioning also has a significant environmental impact, with approximately 117 million metric tons of carbon dioxide being released into the air each year as a result.

Air conditioners operate using similar principles to refrigerators, using energy to transfer heat from the interior of a building to the outside environment. An air conditioner has two main components: an indoor evaporator coil, which cools the air inside the building, and an outdoor condenser coil, which releases the collected heat to the outside. A pump, known as the compressor, moves a heat transfer fluid or refrigerant between the two coils. The refrigerant evaporates in the indoor evaporator coil, drawing heat out of the air and cooling the building. It is then pumped outside to the condenser, where it becomes a gas again and releases its heat to the outside air.

Historically, most air conditioners used chlorofluorocarbons (CFCs) as their refrigerant, but these chemicals are harmful to the ozone layer and CFC production was phased out in the United States in 1995. Currently, most air conditioners use halogenated chlorofluorocarbons (HCFCs) as refrigerants, but the latest type, HCFC-22, began to be phased out in 2010 and was completely banned in 2020. Instead, ozone-safe hydrofluorocarbons (HFCs) and alternative refrigerants such as ammonia are expected to become more prevalent in the market.