Duct Network Designer

Start by calculating total airflow requirements based on cooling/heating loads. Use the equal friction method (0.08-0.1 in.wg/100ft) for most applications. Size main ducts for the total CFM, then size branches proportionally. Account for fittings, turns, and transitions which add equivalent lengths. The calculator handles these complex calculations automatically.

The equal friction method maintains constant pressure loss per unit length throughout the duct system, typically 0.08-0.1 in.wg per 100 feet. This ensures balanced airflow distribution without complex balancing dampers. It's the most common method for commercial HVAC systems and provides predictable system performance.

Fittings (elbows, tees, transitions) create turbulence and pressure drops. Each fitting has an equivalent length value - for example, a 90° elbow equals 10-30 feet of straight duct. The calculator adds these equivalent lengths automatically. Minimizing fittings and using radius elbows reduces energy consumption.

Round ducts have lower pressure loss per CFM (about 30% less than rectangular), are easier to insulate, and have better acoustic performance. Rectangular ducts fit in tight spaces and are easier to fabricate. The calculator provides equivalent round dimensions for rectangular duct sizing.

First, size ducts using the equal friction method for inherent balance. Then install balancing dampers at each branch takeoff. Measure actual airflow at each terminal and adjust dampers to match design values. The calculator helps by showing expected pressure at each branch point.

Main ducts: 1500-2500 FPM for commercial, 600-1200 FPM for residential. Branch ducts: 600-1200 FPM. Higher velocities save duct material but increase noise and energy costs. The calculator warns when velocities exceed recommended limits for the application type.