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Duct Area Formula:
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The HVAC Duct Size Calculator determines the appropriate duct cross-sectional area based on airflow rate (CFM) and air velocity. Proper duct sizing is essential for efficient HVAC system performance and energy conservation.
The calculator uses the duct area formula:
Where:
Explanation: This formula calculates the required duct area to maintain proper airflow at the specified velocity, ensuring optimal system performance.
Details: Correct duct sizing prevents energy waste, reduces noise, maintains proper air distribution, and extends HVAC system lifespan. Undersized ducts increase static pressure and reduce efficiency, while oversized ducts can cause poor air distribution.
Tips: Enter CFM (cubic feet per minute) and desired air velocity in feet per minute. Typical residential velocities range from 600-900 ft/min for supply ducts and 500-700 ft/min for return ducts.
Q1: What is the ideal air velocity for residential HVAC systems?
A: For supply ducts: 600-900 ft/min; for return ducts: 500-700 ft/min. Lower velocities reduce noise but require larger ducts.
Q2: How does duct shape affect the calculation?
A: This calculator provides area. For rectangular ducts, use Area = Width × Height. For round ducts, use Area = π × (Diameter/2)².
Q3: What happens if ducts are undersized?
A: Undersized ducts increase static pressure, reduce airflow, decrease efficiency, increase noise, and can damage HVAC equipment.
Q4: Are there industry standards for duct sizing?
A: Yes, ACCA Manual D is the industry standard for residential duct design, considering friction rate and equivalent length.
Q5: Can this calculator be used for commercial systems?
A: Yes, but commercial systems often have different velocity requirements and may require more complex calculations for large systems.