Hvac Trunk Size Calculator

Introduction: Welcome to the HVAC Trunk Size Calculator, a tool designed to assist you in finding the ideal trunk size for your HVAC system. This article introduces the calculator, highlighting its importance in achieving efficient airflow within the ductwork.

Formula: The HVAC Trunk Size Calculator uses a formula based on total duct length, required airflow, and duct velocity. These factors contribute to the calculation of the optimal trunk size necessary for maintaining proper airflow.

How to Use:

  1. Enter the total duct length in feet.
  2. Input the required airflow in cubic feet per minute (CFM).
  3. Specify the desired duct velocity in feet per minute (FPM).
  4. Click the “Calculate” button to obtain the recommended HVAC trunk size.

Example: For instance, with a total duct length of 50 ft., required airflow of 800 CFM, and a duct velocity of 700 FPM, the calculation would be: √((800 * 50) / 700) = 8.12 inches. Therefore, the recommended HVAC trunk size is 8.12 inches.


  1. Q: What is HVAC trunk size? A: HVAC trunk size refers to the cross-sectional dimensions of the main duct that distributes air to various branches in the HVAC system.
  2. Q: Why is proper trunk size important? A: Proper trunk sizing ensures balanced airflow, preventing issues such as uneven temperature distribution and system inefficiency.
  3. Q: Can I use this calculator for both residential and commercial HVAC systems? A: Yes, the calculator is suitable for both residential and commercial applications.
  4. Q: Is there a standard duct velocity? A: Duct velocity may vary, but typical values range from 600 to 900 FPM. The calculator allows you to input your specific velocity requirement.
  5. Q: How often should HVAC trunk size be calculated? A: It’s recommended to recalculate trunk size when making significant changes to the HVAC system, such as adding new branches or modifying ductwork.

Conclusion: In conclusion, the HVAC Trunk Size Calculator is an invaluable tool for individuals seeking to optimize the performance of their HVAC systems. Accurate trunk sizing contributes to efficient airflow, ensuring a comfortable and evenly conditioned space. Utilize this calculator for both residential and commercial applications to maintain a well-balanced HVAC system.

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