Duct System Design involves sizing and routing air distribution pathways that deliver conditioned air from HVAC equipment to building spaces while maintaining airflow velocity, static pressure, and noise within acceptable limits. Proper duct design ensures even temperature distribution, prevents excessive noise, minimizes energy losses, and provides accessible locations for future cleaning and maintenance. Duct design follows ASHRAE Standards 62.1 for ventilation requirements and 90.1 for efficiency.
Design Specifications
Duct sizing requires calculating airflow in cubic feet per minute (CFM) for each room based on load calculations and ventilation code requirements. Main ducts typically operate at 600 to 800 feet per minute (FPM) velocity while branch ducts limit velocity to 300 to 400 FPM to control noise. Static pressure drops of 0.1 inches of water column per 100 feet of duct length represent acceptable design standards. Insulation values typically range from R-6 to R-13 depending on duct location and climate.
Practical Considerations
Well-designed duct systems reduce fan energy consumption by 20 to 30% compared to oversized or poorly routed designs. Proper sealing to achieve less than 5% leakage prevents conditioned air loss and improves comfort uniformity. Strategic placement of ducts in conditioned spaces rather than attics or crawlspaces reduces temperature stratification and seasonal efficiency losses.