1. What is the McQuay Duct Sizer?

The McQuay duct sizing methodology calculates the required duct cross-sectional area based on airflow (CFM) and desired air velocity. This fundamental HVAC calculation ensures proper air distribution in ventilation systems.

2. How Does the Calculator Work?

The calculator uses the duct sizing formula:

Where:

• \( A \) — Duct cross-sectional area (square feet)
• \( CFM \) — Airflow in cubic feet per minute
• \( V \) — Air velocity in 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 is critical for efficient HVAC system operation, ensuring adequate airflow while minimizing pressure drops and noise.

4. Using the Calculator

Tips: Enter CFM (typically 300-2000 for residential systems) and desired velocity (typically 600-1200 fpm for main ducts). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What are typical velocity limits for ductwork?
A: Main ducts: 1000-2000 fpm, branch ducts: 600-900 fpm, residential: 600-900 fpm for quiet operation.

Q2: How does this relate to duct diameter?
A: For circular ducts, diameter can be calculated from area using \( D = 2 \times \sqrt{A/\pi} \).

Q3: What factors affect duct sizing beyond this calculation?
A: Duct material, length, number of bends, static pressure, and system efficiency requirements.

Q4: When should I use rectangular vs round ducts?
A: Round ducts are more efficient (less friction), while rectangular ducts fit better in tight spaces.

Q5: Are there standard duct sizes?
A: Yes, but they vary by region and application. Common residential sizes include 4", 6", 8", 10", and 12" diameters.