1. What is HVAC Duct Sizing?

HVAC duct sizing is the process of determining the proper dimensions for air distribution ducts in heating, ventilation, and air conditioning systems. Proper sizing ensures efficient airflow 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 calculates the required duct area based on desired airflow and velocity. Lower velocities are typically used for quieter systems, while higher velocities allow for smaller ducts.

3. Importance of Proper Duct Sizing

Details: Correct duct sizing is crucial for system efficiency, proper air distribution, noise control, and energy conservation. Undersized ducts increase static pressure and reduce airflow, while oversized ducts can lead to poor air distribution and higher installation costs.

4. Using the Calculator

Tips:

• For residential systems, typical air velocities range from 600-900 fpm for main ducts and 500-700 fpm for branch ducts
• Commercial systems often use higher velocities (1000-2000 fpm)
• Enter CFM based on your system's airflow requirements
• Select velocity based on application and noise requirements

5. Frequently Asked Questions (FAQ)

Q1: What's the typical velocity for residential HVAC systems?
A: For quiet operation, 600-800 fpm is common for main ducts, with lower velocities (500-600 fpm) for branch runs near occupied spaces.

Q2: How does duct shape affect sizing?
A: Round ducts are more efficient than rectangular ones. When using rectangular ducts, maintain an aspect ratio (width:height) no greater than 4:1 for optimal performance.

Q3: What about duct material and friction losses?
A: This calculator provides basic sizing. For complete design, consider duct material roughness and use ductulator tools or software that account for friction losses.

Q4: How do I convert area to round duct diameter?
A: Diameter = 2 × √(Area/π). For rectangular ducts, choose dimensions that maintain the calculated area while considering space constraints.

Q5: When should I consult a professional?
A: For complex systems, commercial applications, or when dealing with long duct runs with multiple fittings, professional HVAC design is recommended.