Central air conditioners circulate cool air through a system of supply and return ducts. Supply ducts and registers (i.e., openings in the walls, floors, or ceilings covered by grills) carry cooled air from the air conditioner to the home. This cooled air becomes warmer as it circulates through the home; then it flows back to the central air conditioner through return ducts and registers.
If you have a central air system in your home, set the fan to the “auto” mode. In other words, don’t use the system’s central fan to provide air circulation — use circulating fans in individual rooms.
Air conditioners dehumidify the air to improve comfort. However, in extremely humid climates, when outdoor temperatures are moderate, or in cases where the air conditioner is oversized, the air may not reach a low enough humidity to achieve a comfortable level. In those instances, homeowners may reduce the thermostat setting or use a dehumidifier. But in both cases this will increase energy use, both for the dehumidifier itself and because the air conditioner will require more energy to cool the house.
Types of Central Air Conditioners
A central air conditioner is either a split-system unit or a packaged unit.
In a split-system central air conditioner, an outdoor cabinet contains the outdoor heat exchanger, fan, and compressor, and an indoor cabinet contains the indoor heat exchanger and blower. In many split-system air conditioners, the indoor cabinet may contain the a furnace or the indoor heat exchanger of a heat pump. If your home already has a furnace but no air conditioner, a split-system may be the most economical central air conditioner to install.
In a packaged central air conditioner, the heat exchangers, compressor, fan, and blower are all located in one cabinet, which usually is placed on a roof or on a concrete slab next to the house’s foundation. This type of air conditioner also is used in small commercial buildings. The supply and return ducts come from indoors through the home’s exterior wall or roof to connect with the packaged air conditioner. Packaged air conditioners often include electric heating coils or a natural gas furnace. This combination of air conditioner and central heater eliminates the need for a separate furnace.
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