Adding central air conditioning to a home with an existing forced-air heating system is a common and feasible home improvement project. A forced-air system uses a furnace and a network of ducts to distribute heated air throughout the house. This existing infrastructure can be leveraged for cooling by integrating new cooling components with the current heating setup. This retrofit creates a complete, year-round climate control system without requiring the extensive construction of entirely new ductwork.
Key Components and the Retrofit Process
Adding central air conditioning primarily involves installing two major new pieces of hardware that work together to cool the air. The evaporator coil is the indoor component responsible for absorbing heat from the air. This coil is typically installed directly above the furnace within the main air chamber, allowing the furnace’s blower to push cooled air into the existing ductwork.
The second major component is the condenser unit, which is installed outside the home and contains the compressor, condenser coil, and a fan. The compressor pressurizes the refrigerant, which travels through insulated lines connecting the indoor evaporator coil and the outdoor condenser unit. The condenser unit releases the heat absorbed from the indoor air into the outside environment. A condensate line is also installed to drain the water vapor removed from the air during cooling and dehumidification. The existing thermostat often needs to be replaced with a modern version capable of controlling both the heating and cooling functions.
The Role of Ductwork and Sizing
The efficiency of the new air conditioning system depends heavily on assessing the existing ductwork and properly sizing the new unit. Ductwork designed only for heating may not be ideal for cooling, as cooled air requires a higher volume of airflow to be distributed effectively. Professionals must check the ducts for air leaks, which are common in older homes, and seal them to prevent the loss of cool air and maintain system efficiency.
The furnace’s blower motor must be evaluated to ensure it has the capacity to move the necessary volume of air across the new evaporator coil. If the existing blower is undersized, it can restrict airflow, leading to poor cooling performance or causing the evaporator coil to freeze. In such cases, upgrading or replacing the blower or the entire furnace may be necessary to support the cooling load.
The Manual J load calculation is a standardized procedure that determines the exact size, or tonnage, of the AC unit required for the home. This calculation considers factors like the home’s square footage, insulation levels, window types, and local climate. This prevents the installation of an improperly sized unit, which would lead to inefficiency and poor dehumidification.
Cost Factors and the Professional Advantage
The total cost for adding central air conditioning to a forced-air system varies significantly, typically ranging up to $11,500 or more, depending on the project’s complexity. Factors influencing the price include the size and energy efficiency rating of the new AC unit and the extent of necessary ductwork modifications or sealing. Extensive ductwork repair or replacement, or replacing the existing furnace blower, can add thousands of dollars to the overall project cost.
This installation is not a suitable do-it-yourself project and requires professional expertise. Specialized tools and knowledge are needed for handling regulated refrigerants, which can be dangerous if mishandled. The installation involves complex electrical wiring and the precise charging of the system with refrigerant, which directly impacts performance and longevity. Professional installation is also often required to maintain the manufacturer’s warranty and ensure compliance with local building codes and permit requirements.