How do I design an efficient duct network for HVAC systems?

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.

What is the equal friction method in duct sizing?

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.

How do duct fittings affect pressure loss?

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.

What's the difference between round and rectangular ducts?

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.

How do I balance a duct network?

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.

What velocity should I use in duct design?

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.

Duct Network Designer

Design HVAC duct systems with automatic sizing, pressure drop calculations, and critical path analysis. Essential for fan selection and system balancing.

ASHRAESMACNAAuto-SizingCritical Path

Duct Network Configuration

Define your duct network with nodes (terminals) and ducts to calculate airflow distribution and pressure requirements.

About Duct Network Design

The Duct Network Designer uses tree-topology analysis to size ducts and calculate system pressure requirements. It identifies the critical path for fan selection and validates duct velocities against ASHRAE/SMACNA standards.

Key Concepts

Critical Path: Route with highest pressure drop - determines fan sizing
Velocity Method: Size ducts to maintain target air velocity
Equal Friction: Constant pressure drop per meter simplifies balancing
Fitting Losses: K-factors for elbows, tees, transitions

Key Formulas

Darcy-Weisbach::

\Delta P = f \cdot \frac{L}{D_h} \cdot \frac{\rho v^2}{2}

Velocity Pressure::

P_v = \frac{\rho v^2}{2}

Hydraulic Diameter::

D_h = \frac{4A}{P} = \frac{2WH}{W+H}

Interactive Network Diagram

Visualize duct network topology, airflow distribution, and pressure drops

Duct Network Designer

Network Setup

Sizing Method

Air Properties

Options