1. What is the Duct Area Formula?

The duct area formula calculates the cross-sectional area of a duct needed to handle a specific airflow (CFM) at a given velocity. It's fundamental in HVAC system design to ensure proper airflow while minimizing pressure drop and noise.

2. How Does the Calculator Work?

The calculator uses the basic duct area equation:

Where:

• \( A \) — Duct cross-sectional area (square feet)
• \( CFM \) — Airflow rate (cubic feet per minute)
• \( V \) — Air velocity (feet per minute)

Explanation: The equation balances airflow requirements with velocity constraints to determine appropriate duct sizing.

3. Importance of Duct Sizing

Details: Proper duct sizing is crucial for efficient HVAC operation. Undersized ducts increase velocity, causing noise and pressure drop. Oversized ducts increase material costs and may lead to poor air distribution.

4. Using the Calculator

Tips:

• Typical velocity ranges: 600-900 fpm for supply, 500-700 fpm for return
• Higher velocities for shorter runs, lower for longer runs
• Consider noise limitations in occupied spaces

5. Frequently Asked Questions (FAQ)

Q1: What are typical velocity limits?
A: Residential: 600-900 fpm (supply), 500-700 fpm (return). Commercial: up to 1200-1500 fpm in mains, lower in branches.

Q2: How does this relate to round ducts?
A: For round ducts, use \( D = \sqrt{\frac{4A}{\pi}} \) to find diameter after calculating area.

Q3: What about rectangular ducts?
A: For rectangular ducts, maintain aspect ratio (width:height) typically between 1:1 to 4:1 for optimal performance.

Q4: Should I account for friction loss?
A: Yes, after initial sizing, verify pressure drop using duct friction charts or software.

Q5: What's the maximum recommended velocity?
A: Generally 1500 fpm for mains, 1000 fpm for branches in commercial systems, lower for residential.