Central Air Conditioning Sizes

British Thermal Units

• The British thermal unit is the world's standard measure for heat energy. One BTU is equal to the amount of heat needed to raise the temperature of 1 pound of water by 1 degree Fahrenheit, according to the University of Maine. The purpose of a central air conditioner is to remove heat energy from a house's rooms and replace it with cool, fresh air from the outdoors.

Over- and Undersizing

• If homeowners purchase units with too large of a size for their home, they may spend more money than they need. Also, central air conditioners run the risk of dehumidifying a house if they are too large. Central air conditioning units that are too small have problems cooling down houses on hot days. Energy Star says that houses between 1,000 to 1,500 square feet need central air conditioners with a size ranging between 18,000 to 24,000 BTUs, while 2,000- to 2,500-square-foot houses need central air conditioners with at least 34,000 BTUs.

Split System

• Split system central air conditioners have two parts, outdoor metal cabinets and indoor cabinets. The split system air conditioner's compressor and condenser unit is in the unit's outdoor metal cabinet, while the indoor cabinet features the evaporator. Some split system air conditioners also have furnaces and heat pumps in the unit's indoor cabinet. The amount of BTUs in split system air conditioners varies between models. The Goodman SSX14 split air system has a sizing of 18,000 to 56,000 BTUs per hour. The York Affinity CZH system's size is 2 to 5 tons, or 24,000 to 60,000 BTUs. The Bryant Evolution System split air system also features a sizing of 2 to 5 tons.

Packaged

• Packaged central air conditioners only have one cabinet, which is where the compressor, evaporator and condenser are all located. The cabinet of a packaged air conditioner is outside the building; the unit is usually on the roof or on a concrete slab beside one of the building's walls. The building receives air from a series of ducts and vents that are connected to the outside cabinet. The Amana GPC15M has a cooling capacity of 24,000 to 45,500 BTUs per hour. Some of Rheem's packaged air conditioners, such as the RSNL and RSNM, have a sizing of 2 to 5 tons.