Hvac Duct Calculator
Calculate the required duct size for HVAC systems based on airflow and friction loss. This tool helps HVAC professionals and DIY enthusiasts determine the appropriate round or rectangular duct dimensions for efficient air distribution.
Published by:
isCalculator Editorial Team
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How to Use the HVAC Duct Calculator
This calculator determines the required duct size for a given airflow and friction loss. Follow these steps:
- Enter Airflow (CFM): Input the desired airflow in cubic feet per minute (e.g., 400). Must be a positive number.
- Enter Friction Loss (in/100ft): Input the friction loss rate in inches per 100 feet of duct (e.g., 0.1). Must be a positive number.
- Select Duct Type: Choose either Round or Rectangular from the dropdown.
- If Rectangular: Set the Aspect Ratio (width/height, must be ≥ 1, e.g., 2). This field appears only when Rectangular is selected.
- Click "Calculate": The result will display the required duct size:
- For Round: Diameter in inches (e.g., 10.23 in).
- For Rectangular: Width x Height in inches (e.g., 14.00 x 7.00 in).
Note: All inputs are in imperial units (CFM, inches). Ensure values are positive. The formula used is based on standard HVAC duct sizing equations.
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Frequently Asked Questions
It calculates the required round duct diameter or rectangular duct dimensions based on airflow (CFM) and friction loss (in/100ft) for efficient HVAC system design.
Airflow is in CFM (cubic feet per minute), friction loss in inches of water per 100 feet, and dimensions in inches.
The calculator uses standard engineering formulas (ASHRAE fundamentals) for duct sizing. However, always consult with a professional for final design.