1. What is an HVAC Air Flow Calculator?

Definition: This calculator estimates the air flow rate in HVAC systems based on air velocity and duct cross-sectional area.

Purpose: It helps HVAC professionals and engineers determine the air flow rate in gallons per minute (GPM) equivalent or cubic feet per minute (CFM).

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( Q \) — Air flow rate (GPM equivalent)
• \( V \) — Air velocity (feet per second)
• \( A \) — Duct cross-sectional area (square feet)
• 448.83 — Conversion factor (ft³/s to GPM)

Explanation: The formula converts velocity and area measurements into a volumetric flow rate suitable for HVAC system design.

3. Importance of Air Flow Calculation

Details: Proper air flow estimation ensures efficient HVAC system operation, proper ventilation, and energy efficiency in buildings.

4. Using the Calculator

Tips: Enter the air velocity in ft/s and duct area in ft². Both values must be > 0 for accurate calculations.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between GPM and CFM in HVAC?
A: GPM (gallons per minute) measures liquid flow, while CFM (cubic feet per minute) measures air flow. This calculator provides GPM equivalent for comparison purposes.

Q2: What's a typical air velocity in HVAC ducts?
A: Residential systems typically use 700-900 ft/min (11.7-15 ft/s), while commercial systems may use up to 2000 ft/min (33.3 ft/s).

Q3: How do I measure duct area?
A: For rectangular ducts: width × height. For circular ducts: π × (radius)². Convert to square feet by dividing by 144 for inches.

Q4: Why is 448.83 the conversion factor?
A: It converts cubic feet per second to gallons per minute (1 ft³/s = 448.83 GPM).

Q5: Can I use this for CFM calculations?
A: Yes, simply multiply V × A × 60 (for ft³/min) instead of using the GPM conversion factor.