1. What is Ductwork Calculation?

The ductwork calculation determines the appropriate cross-sectional area of ducts in HVAC systems based on airflow rate (CFM) and desired air velocity. Proper duct sizing is essential for efficient system operation and occupant comfort.

2. How Does the Calculator Work?

The calculator uses the fundamental ductwork 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 minimum duct size needed.

3. Importance of Duct Sizing

Details: Proper duct sizing ensures adequate airflow while minimizing noise, energy consumption, and static pressure losses. Undersized ducts reduce system efficiency and increase operating costs.

4. Using the Calculator

Tips: Enter CFM (based on heating/cooling load) and desired velocity (typically 600-900 fpm for supply, 500-700 fpm for return). 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 formula gives area - for rectangular ducts, choose dimensions that maintain aspect ratio while achieving the required area.

Q3: What's the relationship between velocity and pressure drop?
A: Pressure drop increases with the square of velocity - higher velocities require more fan energy to overcome friction losses.

Q4: Should I account for duct insulation?
A: This calculation doesn't include insulation factors - consult duct sizing charts for insulated duct requirements.

Q5: How does altitude affect duct sizing?
A: At higher altitudes, air is less dense - you may need larger ducts or higher velocities to move the same mass of air.