The efficiency and effectiveness of HVAC systems are significantly influenced by the proper sizing of ducts. Incorrectly sized ducts can lead to increased energy consumption, reduced system lifespan, and occupant discomfort. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has been at the forefront of providing guidelines and standards for optimal HVAC design, including duct sizing.
The duct is sized for a constant pressure loss per unit length (e.g., 0.1 inches of water column per 100 feet). ashrae duct size calculator free download
Several software companies offer "free versions" of their paid ductulators to entice you to buy their full suite. The efficiency and effectiveness of HVAC systems are
If you prefer a web-based or simplified tool for quick estimates: Technical Apps from ASHRAE | ashrae.org reduced system lifespan