Duct Air Leakage Testing (DALT)

Air duct leakage is the leakage of air from the air distribution system ductwork. The leakage can occur at joints, seams, and penetrations. Research shows that air duct leakage can be represented as a function of duct surface area, leakage class, and static pressure. Leakage class is determined by the construction methods employed in duct fabrication in accordance with the ANSI/SMACNA HVAC Duct Construction Standards.

Equipment and accessory air leakage is the air leakage associated with HVAC equipment and all other inline accessories such as VAV boxes, fire dampers, control/volume dampers, access doors, etc.

ASHRAE Standard 193 provides standardized methods to test for equipment leakage, and ASHRAE Standard 130 provides leakage tests for VAV boxes. In most cases it is not practical to seal these components “air tight” since they must be accessible for service and field adjustments.

Kitchen Exhaust Hood Testing and Balancing

Because system air leakage is the combination of duct, equipment, and accessory air leakage it is usually impractical or impossible to test the entire system as a whole. Where testing is desired or economically justified, the duct must be tested by logical subsystems.

Leakage requirements shall not be an arbitrary value and shall be assigned on the basis of:

  • Static Pressure

  • Construction
  • Type of duct
  • Research and experience

Why do we need a duct leakage test?

The idea behind it is that the more air that leaks out of the duct system, the more potential energy loss can occur. Because of this, a pressure test is performed on the duct system itself to determine if the duct system is meeting the standards of today’s building codes. Leaking ducts can reduce HVAC system efficiency by as much as 40%. Unless you inspect a duct system for leaks, you may never know how much efficiency (and money) is being lost. This simple, yet effective testing can save a great deal of money, so it is of value to building owners.


An application, known as the total duct leakage test, creates a negative pressure condition on the duct system, and air handler if installed. By applying negative pressure, it is easier to determine the amount of air leaking through the system when measured at strategic locations. If a strong positive pressure was applied, quantifying the volume of leakage would be more difficult. This test is done with a specific fan, air measuring equipment, and tape for sealing registers and grills.

Once the test is done, the system either passed or failed. If passed, the information is submitted as a report for future check. If the test failed, all HVAC connections are checked and resealed where required. Contractors usually know where problem areas are and work on them first.

A well-sealed duct system with an energy efficient heat pump or furnace can pay back big dividends in reduced energy cost. When an installed system meets these requirements, our carbon footprint is lower, and our profession is a little greener.



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