1. What is HVAC Air Flow Measurement?

Definition: This calculator determines the volumetric flow rate of air in cubic feet per minute (CFM) through HVAC ducts.

Purpose: It helps HVAC technicians and engineers properly size and balance air distribution systems.

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 of duct (square feet)
• \( 60 \) — Conversion factor (seconds to minutes)

Explanation: The formula converts velocity in feet per second to volumetric flow in cubic feet per minute by accounting for the duct area and time conversion.

3. Importance of Air Flow Measurement

Details: Proper air flow calculation ensures efficient HVAC system operation, proper ventilation, and occupant comfort while minimizing energy costs.

4. Using the Calculator

Tips: Measure air velocity with an anemometer and duct dimensions to calculate area. Enter both values (must be > 0) to get CFM.

5. Frequently Asked Questions (FAQ)

Q1: How do I measure air velocity?
A: Use a calibrated anemometer at multiple points across the duct face and calculate the average velocity.

Q2: What's a typical air velocity in ducts?
A: Residential systems typically range 600-900 ft/min (10-15 ft/s), while commercial systems may go up to 1200-1800 ft/min (20-30 ft/s).

Q3: How do I calculate duct area?
A: For rectangular ducts: A = width × height. For round ducts: A = π × (diameter/2)².

Q4: Why convert to CFM?
A: CFM is the standard unit for HVAC air flow measurement and system design specifications.

Q5: Does this account for system losses?
A: No, this calculates theoretical flow. Actual system flow may be lower due to friction, bends, and other losses.