ACCA Manual T establishes procedures for selecting proper ductwork sizing, air distribution design, and balancing in residential HVAC systems. This Air Conditioning Contractors of America publication builds on load calculations to ensure efficient air delivery throughout the home. Proper duct design directly influences system efficiency, noise levels, and occupant comfort.
Duct Design and Sizing Procedures
ACCA Manual T specifies the equal friction method and velocity method for duct sizing, maintaining air velocities between 700 and 900 feet per minute in main ducts and 500 to 700 feet per minute in branches. The standard requires friction loss calculations limiting ductwork pressure drop to 0.10 inches of water column per 100 feet of duct. Proper sizing prevents excessive noise, minimizes energy losses, and ensures balanced airflow distribution to all conditioned spaces.
Installation and Commissioning
Manual T addresses register and grille selection, return air path design, and supply duct placement. The procedure includes field balancing with dampers to achieve target airflow rates measured in CFM at each register. Compliance prevents common problems including cold spots, stratification, and equipment short-cycling. Properly designed distribution systems deliver consistent temperature control, reduce ductwork leakage, and achieve the efficiency potential designed into the equipment.