1. What is the Ductwork Sizing Equation?

The duct area equation calculates the required cross-sectional area of HVAC ductwork based on airflow rate (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 rate (cubic feet per minute)
• \( V \) — Air velocity (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 consumption, reduces noise, and maintains system efficiency. Undersized ducts increase static pressure while oversized ducts waste materials and space.

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, High-velocity systems: 1000-2000 fpm.

Q2: How does duct shape affect sizing?
A: Round ducts are more efficient than rectangular. Equivalent round diameter can be calculated for rectangular ducts.

Q3: What about duct material friction losses?
A: This calculator provides basic sizing. Actual design should account for material roughness using the Darcy-Weisbach equation.

Q4: How does altitude affect duct sizing?
A: At higher altitudes, air density decreases, requiring adjustments to CFM calculations.

Q5: What's the relationship between duct size and pressure drop?
A: Smaller ducts increase velocity and pressure drop, requiring more fan energy to move air.