1. What is CFM?

CFM (Cubic Feet per Minute) is a measurement of airflow volume, indicating how much air flows through a duct or system in one minute. It's a crucial parameter in HVAC system design and analysis.

2. How Does the Calculator Work?

The calculator uses the basic CFM formula:

Where:

• \( Velocity \) — Air velocity in feet per minute (fpm)
• \( Area \) — Cross-sectional area of the duct in square feet (ft²)

Explanation: The formula calculates the volume of air moving through a duct by multiplying the speed of the air by the cross-sectional area of the duct.

3. Importance of CFM Calculation

Details: Proper CFM calculation is essential for designing efficient HVAC systems, ensuring adequate ventilation, and maintaining proper air balance in buildings.

4. Using the Calculator

Tips: Enter velocity in feet per minute and area in square feet. Both values must be positive numbers. For round ducts, area = π × radius².

5. Frequently Asked Questions (FAQ)

Q1: What is a typical velocity range for ductwork?
A: For residential systems, 600-900 fpm is common for main ducts, while 500-700 fpm is typical for branch ducts.

Q2: How do I measure duct area?
A: For rectangular ducts: width × height. For round ducts: π × (radius)². Convert all measurements to feet before calculating.

Q3: What CFM is needed per square foot?
A: This varies by application, but a common rule is 1 CFM per square foot for residential cooling, adjusted for climate and building characteristics.

Q4: How does CFM relate to air changes per hour?
A: Air changes = (CFM × 60) / room volume. Typical spaces need 4-6 air changes per hour for good ventilation.

Q5: What affects CFM requirements?
A: Factors include room size, occupancy, heat-generating equipment, window area, and building insulation.