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Streamlining HVAC Efficiency Calculator: Understanding Duct Leakage Calculation

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Efficiency is the backbone of a well-functioning HVAC system, and one key aspect of this is managing duct leakage. Duct leakage represents a significant energy loss and can negatively impact your HVAC system’s performance. With our Duct Leakage Calculator, you can quickly estimate the leakage in your system, a crucial step in improving its overall efficiency.

What is Duct Leakage?

Duct leakage is the air that escapes from the duct system in your HVAC unit. It can occur at various points, such as seams and joints, or through holes and cracks. This leakage not only reduces the system’s efficiency but can also affect indoor air quality.

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The formula to calculate duct leakage is:

Leakage (CFM) = Leakage Class * Duct Surface Area * sqrt(Pressure Difference)

Using the Duct Leakage Calculator

To use our Duct Leakage Calculator, you will need to input the following:

  1. Duct Surface Area (in square feet): This is the total surface area of the ducts in the system.
  2. Leakage Class (CFM/sq. ft. at 1″ wg): This is a rating that quantifies the leakiness of the ducts.
  3. Pressure Difference (in inches of water gauge): This is the difference in pressure inside the duct compared to outside it.

Once these values are inputted, press ‘Calculate’ to estimate the duct leakage in CFM (cubic feet per minute).

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An Example of a Duct Leakage Calculation

Let’s say you have a duct system with the following parameters:

  • Duct Surface Area: 200 square feet
  • Leakage Class: 0.5 CFM/sq. ft. at 1″ wg
  • Pressure Difference: 1.0 inches of water gauge

Plugging these values into the calculator:

Leakage (CFM) = 0.5 CFM/sq. ft. * 200 sq. ft. * sqrt(1.0 in wg)

Our calculator would estimate a duct leakage of 100 CFM.


Efficiency is crucial in maintaining an HVAC system, and duct leakage can significantly hinder it. Understanding how to calculate this leakage can help identify areas that need improvement and maintain the overall effectiveness of your system. Our Duct Leakage Calculator is an excellent tool for providing a quick estimation, but remember, for precise measurements and adjustments, consulting with a professional HVAC technician is highly recommended.

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