Return ducts transport air from occupied spaces back to the furnace or air handler for reconditioning. They complete the air circulation cycle by drawing air through return grilles and back to the system. Properly designed return ducts ensure adequate airflow and prevent negative pressure in the home.
System Function
Return ducts must be sized appropriately to handle the same volume as supply ducts, typically one square inch of return duct area per 2 CFM of system capacity. Undersized returns create negative pressure, reducing supply airflow and drawing in unconditioned outside air through cracks and gaps. Multiple return ducts in different zones improve comfort and system efficiency.
Installation Requirements
Return ducts should have smooth interior surfaces to minimize friction losses. Flexible return ducts are acceptable but rigid ducts perform better. Return plenums must be properly sealed and insulated. Adequate return duct openings and filter access ensure system maintenance and prevent airflow restrictions.