Duct Size Formula:
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The duct size formula calculates the required cross-sectional area of an air conditioning duct based on airflow (CFM) and desired air velocity. Proper duct sizing is essential for efficient HVAC system operation.
The calculator uses the basic duct sizing equation:
Where:
Explanation: The formula balances airflow requirements with velocity constraints to determine the minimum duct size needed.
Details: Correct duct sizing ensures proper airflow, minimizes energy loss, reduces noise, and maintains system efficiency. Undersized ducts increase static pressure while oversized ducts can lead to poor air distribution.
Tips:
Q1: What's the recommended air velocity for residential systems?
A: 600-900 fpm for supply ducts and 500-700 fpm for return ducts is typical for residential applications.
Q2: How do I convert square feet to round duct diameter?
A: Use the formula: Diameter = 2 × √(Area/π). A 12"×12" duct (1 sq.ft) ≈ 13.5" diameter round duct.
Q3: What happens if ducts are too small?
A: Undersized ducts cause high velocity, increased noise, reduced airflow, and higher energy consumption.
Q4: Are there standard duct sizes?
A: Yes, common rectangular duct sizes follow 2-inch increments (e.g., 10×4, 12×6, 14×8 inches).
Q5: Should I account for duct friction losses?
A: For precise calculations, yes. This simplified formula gives basic sizing - professional designs include friction rate calculations.