1. What is Nominal Air Flow Rate?

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

Purpose: It helps HVAC professionals and engineers properly size ductwork and select appropriate equipment for ventilation 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 air velocity multiplied by duct area gives flow rate per second, which is then converted to minutes.

3. Importance of Air Flow Rate Calculation

Details: Proper airflow calculation ensures adequate ventilation, proper system performance, energy efficiency, and occupant comfort.

4. Using the Calculator

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

5. Frequently Asked Questions (FAQ)

Q1: What's a typical air velocity for HVAC systems?
A: Typically 700-900 ft/min (12-15 ft/s) for main ducts, 500-700 ft/min for branch ducts.

Q2: How do I measure duct area?
A: For rectangular ducts: width × height. For round ducts: π × (radius)².

Q3: Why convert to CFM?
A: CFM is the standard unit for measuring air flow in HVAC systems in the US.

Q4: What if my duct isn't round or rectangular?
A: Use equivalent diameter calculations or specialized formulas for odd shapes.

Q5: Does this account for pressure drops?
A: No, this is nominal flow rate. System design should consider pressure losses.