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CFM Calculation Formula:
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CFM (Cubic Feet per Minute) calculation for round ducts determines the volume of air flow through a circular duct based on air velocity and duct diameter. This is essential for HVAC system design and analysis.
The calculator uses the CFM formula:
Where:
Explanation: The formula calculates the cross-sectional area of the duct and multiplies it by the air velocity to determine the volumetric flow rate.
Details: Accurate CFM calculation is crucial for proper HVAC system design, ensuring adequate airflow for heating and cooling, maintaining indoor air quality, and optimizing energy efficiency.
Tips: Enter air velocity in ft/min and duct diameter in inches. The diameter is preset to 14 inches for standard 14" round duct calculations. All values must be positive numbers.
Q1: What is a typical velocity for HVAC ductwork?
A: Residential systems typically use 600-900 ft/min, while commercial systems may use 1000-2000 ft/min, depending on application and noise considerations.
Q2: Why is the diameter divided by 2 in the formula?
A: Dividing diameter by 2 converts it to radius, which is needed to calculate the circular cross-sectional area (πr²).
Q3: How does duct size affect CFM?
A: Larger ducts can move more air at lower velocities, reducing friction loss and noise, while smaller ducts require higher velocities to move the same amount of air.
Q4: Can this calculator be used for rectangular ducts?
A: No, this calculator is specifically for round ducts. Rectangular ducts use a different formula based on width and height dimensions.
Q5: What factors affect air velocity in ducts?
A: Fan power, duct length, number of bends, duct roughness, and static pressure all influence the actual air velocity in a duct system.