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Duct Size Formula:
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The duct size calculation determines the appropriate duct diameter based on airflow (CFM) and air velocity. Proper duct sizing is essential for efficient HVAC system performance and energy conservation.
The calculator uses the duct size formula:
Where:
Explanation: The formula calculates the required duct cross-sectional area to maintain the desired air velocity for a given airflow rate.
Details: Correct duct sizing ensures optimal airflow, reduces energy consumption, minimizes noise, and prevents system strain. Undersized ducts increase pressure drop and fan energy, while oversized ducts can lead to poor air distribution.
Tips: Enter CFM in cubic feet per minute and velocity in feet per minute. Both values must be positive numbers. Typical velocity ranges: 600-900 ft/min for low-pressure systems, 1200-1800 ft/min for high-pressure systems.
Q1: What is the ideal air velocity for HVAC ducts?
A: For residential systems, 600-900 ft/min is typical. For commercial systems, 1200-1800 ft/min is common. Lower velocities reduce noise but require larger ducts.
Q2: How does duct shape affect the calculation?
A: This formula calculates equivalent round duct diameter. For rectangular ducts, additional calculations are needed to determine equivalent round size.
Q3: What factors influence CFM requirements?
A: Room size, occupancy, heat load, and system capacity all affect required CFM. Professional load calculations are recommended for accurate sizing.
Q4: Are there standard duct sizes?
A: Yes, ducts typically come in standard sizes (4", 6", 8", 10", 12", etc.). The calculated size should be rounded to the nearest available standard size.
Q5: When should I consult an HVAC professional?
A: For complete system design, complex layouts, or commercial applications, always consult a qualified HVAC engineer to ensure proper system performance.