1. What is a Velocity Pressure to CFM Calculator?

Definition: This calculator converts velocity pressure measurements to cubic feet per minute (CFM) of air flow in duct systems.

Purpose: It helps HVAC professionals and engineers determine air flow rates based on velocity pressure readings.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( Q \) — Air flow rate (cubic feet per minute, CFM)
• \( A \) — Cross-sectional area of duct (square feet)
• \( VP \) — Velocity pressure (inches water gauge)
• \( \rho \) — Air density (pounds per cubic foot)

Explanation: The formula converts velocity pressure to velocity, multiplies by area to get volume flow, and converts units to CFM.

3. Importance of CFM Calculation

Details: Accurate CFM calculations are essential for proper HVAC system design, balancing, and performance verification.

4. Using the Calculator

Tips: Enter duct area in ft², velocity pressure in inches wg, and air density (default 0.075 lb/ft³ for standard air). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is velocity pressure?
A: Velocity pressure is the pressure caused by air movement in a duct, measured in inches of water gauge (in wg).

Q2: What's the standard air density?
A: Standard air density is 0.075 lb/ft³ at 70°F and sea level. Adjust for altitude or temperature differences.

Q3: How do I measure velocity pressure?
A: Use a pitot tube connected to a manometer to measure the difference between total and static pressure.

Q4: Why multiply by 60 and 0.0283168?
A: These factors convert from ft³/sec to ft³/min (CFM) and account for unit conversions in the equation.

Q5: When would I need this calculation?
A: When balancing HVAC systems, designing ductwork, or troubleshooting airflow problems.