1. What is Air Volume Flow Rate?

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

Purpose: It helps HVAC engineers, mechanical designers, and technicians calculate air flow in ventilation systems, ducts, and piping.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( Q \) — Volumetric flow rate (GPM)
• \( V \) — Velocity of air (ft/s)
• \( A \) — Cross-sectional area (ft²)
• 448.83 — Conversion factor (cubic feet per second to GPM)

Explanation: The velocity is multiplied by the area to get cubic feet per second, then converted to GPM.

3. Importance of Air Flow Calculation

Details: Proper air flow calculation ensures efficient system design, adequate ventilation, and proper equipment sizing.

4. Using the Calculator

Tips: Enter the air velocity in feet per second and the cross-sectional area in square feet. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: Why convert to GPM when measuring air?
A: GPM provides a standardized unit that can be compared with liquid flow rates in combined systems.

Q2: What's a typical air velocity in ducts?
A: Typically 800-1200 ft/min (13.3-20 ft/s) for main ducts, lower for branch ducts.

Q3: How do I measure duct area?
A: For circular ducts: \( \pi \times r^2 \). For rectangular ducts: width × height.

Q4: Does this account for pressure changes?
A: No, this is for ideal conditions. Actual flow may vary based on system pressure.

Q5: Can I use this for liquid flow?
A: Yes, but remove the conversion factor (use \( Q = V \times A \)) for direct ft³/s calculation.