1. What is the Duct Area Formula?

The duct area formula calculates the required cross-sectional area of a duct based on airflow (CFM) and air velocity. It's essential for designing efficient HVAC systems with proper airflow and minimal pressure drop.

2. How Does the Calculator Work?

The calculator uses the duct area formula:

Where:

• \( CFM \) — Airflow in cubic feet per minute
• \( Velocity \) — Air velocity in feet per minute

Explanation: The formula determines the necessary duct cross-sectional area to maintain the desired air velocity for a given airflow rate.

3. Importance of Proper Duct Sizing

Details: Correct duct sizing ensures efficient airflow, reduces energy consumption, minimizes noise, and maintains proper system pressure. Undersized ducts increase static pressure while oversized ducts reduce air velocity.

4. Using the Calculator

Tips: Enter CFM (typically 300-2000 for residential systems) and desired velocity (typically 600-900 ft/min for supply, 500-700 ft/min for return). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What are typical air velocities for HVAC systems?
A: Supply ducts: 600-900 ft/min, Return ducts: 500-700 ft/min, Commercial systems may use higher velocities.

Q2: How does duct shape affect the calculation?
A: The formula calculates area - for rectangular ducts, you'll need to determine appropriate width/height combinations that provide the same area.

Q3: What's the relationship between velocity and pressure drop?
A: Higher velocities increase friction and pressure drop, requiring more fan energy. The ideal balance depends on system requirements.

Q4: Should I include safety factors in my calculation?
A: Many designers add 10-20% to the calculated area to account for future system changes or installation factors.

Q5: How does this relate to duct diameter for round ducts?
A: For round ducts, use the formula: Diameter = 2 × √(Area/π)