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Duct Size Equation:
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The duct size equation calculates the appropriate diameter for HVAC ductwork based on airflow rate, velocity, and a conversion factor. Proper duct sizing is essential for efficient and effective HVAC system operation.
The calculator uses the duct size equation:
Where:
Explanation: The equation calculates the duct diameter needed to maintain proper airflow at the specified velocity, with the factor accounting for unit conversion and system characteristics.
Details: Correct duct sizing ensures optimal HVAC system performance, proper air distribution, energy efficiency, and noise reduction. Undersized ducts can cause high static pressure and reduced airflow, while oversized ducts can lead to poor air distribution and increased installation costs.
Tips: Enter flow rate in cfm, velocity in fpm, and the appropriate factor for your system. All values must be positive numbers. Typical factors range from 1.0 to 1.3 depending on duct shape and material.
Q1: What is a typical velocity for HVAC ducts?
A: For residential systems, typical velocities range from 600-900 fpm for supply ducts and 500-700 fpm for return ducts. Commercial systems may use higher velocities.
Q2: How do I determine the right factor to use?
A: The factor depends on duct shape (round, rectangular) and material. Consult HVAC design manuals or engineering guidelines for appropriate values.
Q3: What happens if ducts are improperly sized?
A: Improper sizing can lead to reduced system efficiency, uneven temperatures, increased noise, higher energy costs, and premature equipment failure.
Q4: Should I consider other factors besides size?
A: Yes, also consider duct material, insulation, layout, and pressure drop calculations for a complete HVAC design.
Q5: Can this calculator be used for both supply and return ducts?
A: Yes, but you may need to use different velocity values and factors for supply versus return ducts.