1. What is the Duct Area Formula?

The duct area formula calculates the required cross-sectional area of HVAC ductwork 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 (ft²)
• \( CFM \) — Airflow in cubic feet per minute
• \( V \) — Air velocity in feet per minute

Explanation: The formula determines the necessary duct size to maintain proper air velocity for a given airflow rate.

3. Importance of Proper Duct Sizing

Details: Correct duct sizing ensures efficient airflow, minimizes energy consumption, reduces noise, and maintains proper system pressure balance.

4. Using the Calculator

Tips: Enter CFM (typically 350-400 CFM per ton of cooling) and desired velocity (typically 600-900 ft/min for supply ducts). 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 ft/min, Return ducts: 500-700 ft/min, Low-velocity systems: 400-600 ft/min.

Q2: How does duct shape affect sizing?
A: Round ducts are more efficient than rectangular. When using rectangular ducts, maintain similar cross-sectional area.

Q3: What happens if ducts are too small?
A: Excessive velocity increases noise, static pressure, and energy consumption while reducing airflow.

Q4: Should I account for duct friction losses?
A: This calculator provides basic sizing. For complete design, consider friction losses using the Darcy-Weisbach equation.

Q5: How does altitude affect duct sizing?
A: At higher altitudes, air is less dense, so CFM values should be adjusted accordingly.