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Duct Area Formula:
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HVAC duct sizing is the process of determining the appropriate cross-sectional area for air distribution ducts in residential heating, ventilation, and air conditioning systems. Proper sizing ensures efficient airflow and system performance.
The calculator uses the duct area formula:
Where:
Explanation: This formula calculates the required duct area based on the desired airflow rate and velocity. Lower velocities typically mean larger ducts but quieter operation.
Details: Correct duct sizing is essential for efficient HVAC operation. Undersized ducts increase static pressure, reduce airflow, and decrease system efficiency. Oversized ducts can lead to poor air distribution and increased installation costs.
Tips: Enter CFM (cubic feet per minute) and desired air velocity (ft/min). Typical residential air velocities range from 600-900 ft/min for supply ducts and 500-700 ft/min for return ducts.
Q1: What is the recommended velocity for residential HVAC ducts?
A: For supply ducts: 600-900 ft/min, for return ducts: 500-700 ft/min. Lower velocities are quieter but require larger ducts.
Q2: How does duct shape affect sizing calculations?
A: Round ducts are more efficient than rectangular ducts. When using rectangular ducts, the aspect ratio (width-to-height ratio) affects airflow characteristics.
Q3: What factors besides CFM affect duct sizing?
A: Duct material roughness, number of bends, length of duct runs, and static pressure requirements all influence optimal duct sizing.
Q4: Should I use the same size for all ducts in a system?
A: No, duct sizes should be calculated for each branch based on the CFM requirements of the areas they serve using manual D calculations.
Q5: How do I convert duct area to round or rectangular dimensions?
A: For round ducts: diameter = 2 × √(area/π). For rectangular ducts, choose an aspect ratio (typically 1:1 to 4:1) and calculate dimensions accordingly.