1. What is the AC Duct Calculator?

The AC Duct Calculator determines the required cross-sectional area of 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 fundamental duct equation:

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 optimal duct size.

3. Importance of Proper Duct Sizing

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

4. Using the Calculator

Tips:

• Typical residential air velocities: 600-900 fpm for supply, 500-700 fpm for return
• Commercial systems often use higher velocities (1000-2000 fpm)
• Enter CFM based on your HVAC system requirements
• All values must be positive numbers

5. Frequently Asked Questions (FAQ)

Q1: What happens if ducts are too small?
A: Undersized ducts cause increased air velocity, resulting in noise, pressure drops, and reduced system efficiency.

Q2: What's the recommended velocity for residential systems?
A: 600-900 fpm for supply ducts and 500-700 fpm for return ducts is typical for residential applications.

Q3: How do I convert square feet to round duct diameter?
A: Use the formula: Diameter = 2 × √(Area/π). A 12" round duct has about 0.785 sq.ft. area.

Q4: Does this calculator work for rectangular ducts?
A: Yes, the area calculation is the same. You'll need to determine appropriate width/height ratios separately.

Q5: What factors affect duct sizing beyond CFM and velocity?
A: Duct material, length, number of bends, and insulation all affect system performance but aren't accounted for in this basic calculation.