Split systems are the most common type of central air conditioner found in this country.

Typically, these systems are found Inside the house, tucked in a cabinet attached to an outside wall, is the evaporator coil, which removes heat and moisture from the air. Outside the house, a metal case contains the condenser coil, which releases the heat, and the compressor, which pumps refrigerant between the two coils.

The indoor component of the air conditioner is connected to a network of ducts, and a blower circulates the cold air through them to reach all areas of the home. This type of system is the most economical to install in a house with a central furnace, because it can utilize the ductwork used by the heating system.

Heat pumps are a variation on the traditional split system. In hot summer months, the unit pumps heat from the house and releases it outside. In the winter, it extracts heat from the outdoor air and uses it to warm the house. One of the greatest advantages of a heat pump system over a standard heating ventilating and air conditioning (HVAC) unit is that there is no need to install separate systems to heat and cool your home. Heat pumps also work extremely efficiently, because they simply transfer heat, rather than burn fuel to create it. Because of that, heat pumps can be used effectively for both heating and cooling in mild climates. However, heat pumps do not work well when temperatures remain below freezing for a long time, so they are not the best choice for climates where the weather is colder.

If you feel that a heat pump is the right choice for you, but you live in a cold climate, a specialized type of heat pump, called a ground-source or geothermal heat pump might be an option. It works by drawing heat out of the ground rather than the air. However, while long-term energy savings can be worthwhile, a geothermal heat pump costs about 40 percent more than other types of heating and cooling systems.

Packaged central air conditioners combine the evaporator, condenser and compressor in a single unit. The air conditioner is usually located on a concrete slab near the foundation or on the roof of the home. Ducts are run through the exterior wall or roof. They work by drawing air from inside the house and returning cooled air indoors. This type of air conditioning system is also used in small commercial buildings. When it is combined with a set of heating coils or a natural gas furnace, it can eliminate the need for a separate furnace inside the building.

Ductless mini-split systems are a great choice for homes that do not have the room for ductwork. Like a basic split system, the ductless mini-split system combines an outdoor compressor and condenser with one or more indoor air-handling units. These units are mounted high on the wall and have blowers attached to them. Tubing connects the indoor and outdoor units and a refrigerant is circulated between them. For a room to be cooled, each room in the home would need to contain one of these indoor units and cools that room only, much like a window air conditioner.

One of the main advantages of ductless mini-split systems is that they can be installed without installing ductwork in the walls or floors. They also allow the flow of cold air to be controlled independently in each room (or shut off altogether in empty rooms to save energy). Due to the high cost of the individual units, if they are used to cool an entire house, mini-split systems are more expensive than ducted central air conditioning systems. However, because they eliminate the energy loss associated with ductwork they are more efficient.