1. What is Duct Cross-Sectional Area?

The duct cross-sectional area is the internal area of an HVAC duct through which air flows. Proper sizing is crucial for efficient air distribution and system performance.

2. How Does the Calculator Work?

The calculator uses the fundamental duct sizing 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 the appropriate duct size.

3. Importance of Proper Duct Sizing

Details: Correct duct sizing ensures efficient airflow, minimizes pressure drops, reduces noise, and optimizes energy consumption in HVAC systems.

4. Using the Calculator

Tips: Enter CFM (airflow rate) and desired air velocity. Typical velocities: 600-900 fpm for main ducts, 500-700 fpm for branch ducts.

5. Frequently Asked Questions (FAQ)

Q1: What is the recommended air velocity for ducts?
A: It varies by application: 600-900 fpm for main ducts, 500-700 fpm for branch ducts, and 300-500 fpm for final runs.

Q2: How does duct shape affect the calculation?
A: The formula calculates area - for round ducts, diameter can be derived from area using \( D = 2 \times \sqrt{A/\pi} \).

Q3: What happens if ducts are undersized?
A: Undersized ducts cause increased velocity, higher pressure drops, reduced airflow, noise, and increased energy consumption.

Q4: Should I consider static pressure in sizing?
A: Yes, this is a basic calculation. Complete duct design should consider static pressure, friction losses, and system effects.

Q5: How does altitude affect duct sizing?
A: At higher altitudes, air is less dense, so CFM values may need adjustment for equivalent mass flow rates.