1. What is the CFM to FPM Conversion?

The CFM to FPM conversion calculates air velocity (feet per minute) in round ducts based on airflow (cubic feet per minute) and duct diameter. This is essential for HVAC system design and analysis.

2. How Does the Calculator Work?

The calculator uses the FPM calculation formula:

Where:

• \( FPM \) — Feet per minute (air velocity)
• \( CFM \) — Cubic feet per minute (airflow)
• \( D \) — Duct diameter in inches
• \( \pi \) — Mathematical constant pi (approximately 3.14159)

Explanation: The formula converts duct diameter from inches to feet, calculates the cross-sectional area of the duct, then divides CFM by the area to determine velocity.

3. Importance of FPM Calculation

Details: Proper air velocity calculation is crucial for efficient HVAC system design, ensuring adequate airflow while minimizing noise and energy consumption.

4. Using the Calculator

Tips: Enter CFM value in cubic feet per minute and duct diameter in inches. Both values must be positive numbers greater than zero.

5. Frequently Asked Questions (FAQ)

Q1: What is the typical FPM range for HVAC systems?
A: Residential systems typically operate at 600-900 FPM, while commercial systems may range from 1000-2000 FPM depending on application.

Q2: Why convert diameter from inches to feet?
A: Since CFM is measured in cubic feet per minute, consistent units (feet) must be used throughout the calculation for accurate results.

Q3: Can this calculator be used for rectangular ducts?
A: No, this calculator is specifically designed for round ducts. Rectangular ducts require a different formula using cross-sectional area.

Q4: What happens if FPM is too high or too low?
A: High FPM can cause excessive noise and pressure drop, while low FPM may lead to inadequate airflow and poor system performance.

Q5: How does duct material affect FPM calculations?
A: While the basic calculation remains the same, different duct materials have varying friction factors that affect actual airflow velocity in practice.