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.