What is necessary for every furnace and fan coil unit?

For every furnace and fan coil unit, a return air duct is essential because it is responsible for drawing the air back from the living space into the heating or cooling system. This process is crucial for maintaining proper airflow, as it ensures that the system operates efficiently by recycling the air. Without a return air duct, the furnace or fan coil would not have a consistent source of air to heat or cool, leading to inefficient operation and potential system damage.

Having the ability to circulate air effectively is vital for achieving the desired temperature and comfort levels in a space. The return air duct also plays a key role in balancing the pressure within the home, helping to prevent issues such as drafts or uncomfortable hot and cold spots. While other components, such as a supply air register, gas line, or exhaust system, may be important for specific types of systems, the return air duct is universally required for the basic operation of every furnace and fan coil unit.