1. What is the HVAC Duct Area Equation?

The HVAC duct area equation calculates the required cross-sectional area of a duct based on airflow (CFM) and desired air velocity. Proper duct sizing is essential for efficient HVAC system operation.

2. How Does the Calculator Work?

The calculator uses the duct area equation:

Where:

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

Explanation: The equation balances airflow requirements with velocity constraints to determine optimal duct size.

3. Importance of Proper Duct Sizing

Details: Correct duct sizing ensures proper airflow, minimizes energy loss, reduces noise, and maintains system efficiency. Undersized ducts increase static pressure while oversized ducts can lead to poor air distribution.

4. Using the Calculator

Tips: Enter CFM based on your HVAC system requirements and select appropriate velocity (typically 600-900 fpm for supply, 500-700 fpm for return air). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What are typical air velocities for different duct types?
A: Supply ducts: 600-900 fpm, Return ducts: 500-700 fpm, Low-velocity systems: 400-600 fpm, High-velocity systems: 1000-2000 fpm.

Q2: How does duct shape affect the calculation?
A: The equation calculates area - for round ducts, convert to diameter using \( D = 2 \times \sqrt{A/\pi} \). Rectangular ducts can use this area to determine width × height.

Q3: What factors affect CFM requirements?
A: Room size, heat load, number of occupants, equipment type, and climate all influence required CFM.

Q4: When should I use higher velocities?
A: Higher velocities may be used in main ducts where space is limited, but consider noise and pressure drop tradeoffs.

Q5: Are there standard duct sizes?
A: Yes, ducts typically come in standard sizes (4", 6", 8", etc.), so round up to the nearest available size after calculation.