1. What is the Air Duct Equation?

The air duct equation (A = CFM/V) calculates the required cross-sectional area of an air duct based on the airflow rate (CFM) and desired air velocity. This fundamental HVAC equation helps in proper duct system design.

2. How Does the Calculator Work?

The calculator uses the basic duct 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 proper duct sizing.

3. Importance of Duct Sizing

Details: Proper duct sizing is crucial for efficient HVAC system operation, ensuring adequate airflow while minimizing noise and energy consumption.

4. Using the Calculator

Tips: Enter CFM (based on your HVAC system requirements) and desired air velocity (typically 600-900 fpm for supply ducts). Both 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: 300-500 fpm.

Q2: How does duct shape affect the calculation?
A: The equation gives area - for round ducts, diameter can be calculated from area (D = 2√(A/π)).

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

Q4: Why is velocity important in duct design?
A: High velocity causes noise and pressure drop, while low velocity may not deliver sufficient airflow.

Q5: Should I include safety factors?
A: Many designers add 10-20% to calculated CFM to account for system losses and future needs.