1. What is an Air Flow Rate CFM Calculator?

Definition: This calculator determines the volumetric flow rate of air in cubic feet per minute (CFM) based on air velocity and cross-sectional area.

Purpose: It helps HVAC professionals, engineers, and technicians calculate air flow for ventilation, duct design, and system analysis.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( Q_{cfm} \) — Air flow rate (cubic feet per minute)
• \( V \) — Air velocity (feet per second)
• \( A \) — Cross-sectional area (square feet)
• 60 — Conversion factor (seconds to minutes)

Explanation: The formula converts velocity in ft/s to volume flow in ft³/min by multiplying by the area and time conversion factor.

3. Importance of Air Flow Rate Calculation

Details: Proper CFM calculation ensures adequate ventilation, proper HVAC system sizing, and efficient air distribution in buildings.

4. Using the Calculator

Tips: Enter the air velocity in ft/s and cross-sectional area in ft². Both values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: How do I measure air velocity?
A: Use an anemometer to measure air speed at various points in the duct and calculate the average velocity.

Q2: What's a typical air velocity in HVAC systems?
A: Residential systems typically range from 300-700 ft/min (5-11.7 ft/s), while commercial systems may go up to 2000 ft/min (33.3 ft/s).

Q3: How do I calculate duct cross-sectional area?
A: For round ducts: \( A = \pi r² \). For rectangular ducts: \( A = width \times height \).

Q4: Why multiply by 60 in the formula?
A: The factor converts seconds to minutes since CFM is cubic feet per minute while velocity is in feet per second.

Q5: Can I use this for liquid flow calculations?
A: The same principle applies, but ensure consistent units (e.g., gallons per minute instead of CFM).