Central Air Conditioning

Central air conditioners circulate cool air through a system of supply and return ducts. Supply ducts and registers (openings in the walls, floors, or ceilings covered by grills) deliver cooled air from the air conditioner to your home. This cooled air becomes warmer as it circulates through the home, then is pulled back to the central air conditioner through return ducts and registers. The central air conditioner’s blower fan is often referred to as the Air Handling Unit (AHU).

How Central Air Conditioners Work

Air conditioners not only cool the air but also dehumidify it to improve comfort. However, in extremely humid climates or when outdoor temperatures are moderate, even correctly sized air conditioners may not achieve comfortable humidity levels. Homeowners may lower the thermostat or use a dehumidifier, which increases energy use for both the dehumidifier and the air conditioner.

For optimal efficiency, set your central air system’s fan to "auto" mode and use circulating fans in individual rooms for additional air circulation.

Types of Central Air Conditioners

Central air conditioners come in two main types: split-system units and packaged units.

Split-System Central Air Conditioners: These have an outdoor unit containing the heat exchanger, fan, and compressor, and an indoor unit with the heat exchanger and blower. If you already have a furnace but no air conditioner, consider installing a heat pump instead of a split-system air conditioner. A heat pump can provide both heating and cooling efficiently.
Packaged Central Air Conditioners: In these systems, the heat exchanger, compressor, fan, and blower are all located in one cabinet, typically placed on a roof or concrete slab next to the house's foundation. Packaged units often include electric heating coils, heat pump heating, or a natural gas furnace, eliminating the need for a separate furnace.

Installation and Location of Air Conditioners

Proper installation is critical for optimal performance and efficiency. Ensure your contractor:

Allows adequate indoor space for installation, maintenance, and repair.
Correctly sizes HVAC equipment using an Air Conditioning Contractors of America (ACCA) Manual J Load Calculation and an ACCA Manual S Equipment Selection protocol.
Uses a duct-sizing methodology such as ACCA Manual D.
Ensures enough supply and return air registers for efficient air distribution.
Installs ductwork within conditioned space whenever possible, not in unconditioned spaces like attics or garages.
Seals all ducts with duct mastic and properly insulates them.
Locates the condensing unit where its noise won't disturb you or your neighbors and where airflow won't be obstructed.
Verifies the correct refrigerant charge and airflow rate as specified by the manufacturer.
Centrally locates the thermostat away from heat sources like windows or supply registers.

Choosing or Upgrading Your Central Air Conditioner

Central air conditioners are more efficient than room air conditioners. They are also out of the way, quiet, and convenient to operate. To save energy and money, buy an energy-efficient model and reduce your central air conditioner's energy use. In an average-sized home, air conditioning can consume more than 2,000 kilowatt-hours of electricity per year, resulting in significant carbon dioxide and sulfur dioxide emissions.

Heat Pumps

Consider a heat pump instead of a traditional air conditioner. Heat pumps provide both heating and cooling and can be more efficient, especially in moderate climates. For more details, explore our comprehensive guide on Heat Pump Systems.

Energy Efficiency Tips

Proper Sizing: Ensure your air conditioner is the correct size for your home. An oversized unit won't adequately remove humidity, while an undersized unit won't cool effectively on the hottest days.
SEER Ratings: Look for a high SEER (Seasonal Energy Efficiency Ratio) rating. Newer systems can have SEER ratings as high as 26.
ENERGY STAR®: Look for the ENERGY STAR and EnergyGuide labels. ENERGY STAR certified units are about 15% more efficient than standard models.
Variable Capacity Systems: Consider variable capacity air conditioning systems. These units run often but usually at very efficient low speeds, offering minimal sound and enhanced dehumidification, especially during spring and fall. This capability leads to exceptional comfort and efficiency.

Take Action

Upgrade to a more efficient central air conditioner or heat pump and ensure proper installation for optimal performance. For more information, explore ENERGY STAR® resources for Central Air Conditioning.