A duct leak test (duct test) can be performed before drywall is placed or after construction. In both cases, the requirements are the same. Five days ago, the system will need to achieve a leak rate of less than 4 CFM (cubic feet per minute) per 100 square feet of the home. If leaks in the ducts are tested at the time of entry, a HERS evaluator must confirm and document that the total leak in the ducts is greater than ≤ 4 CFM 25 per 100 square feet of conditioned floor area or ≤ 40 CFM25 using a test protocol approved by Resnet, and must verify, through visual inspection, that the duct covers are sealed to finish the surfaces at the end. There are many duct sealing systems available that will fill most small openings around duct fittings.
In addition, the evaluator must visually check, in case of rolling, that the ducts are completely insulated (R-8 for supply ducts and R-6 for return ducts and other ducts) along their entire length, including all connections, and that the insulation is not compressed by the presence of tight belts, structural elements or excessive flexion. When all ducts are in conditioned spaces, it is only necessary to perform the total duct leak test if certain conditions are met. Some builders prefer to check the ducts for leaks when entering, when they are easier to access, in case there is an additional need to seal the air. A duct air leak test will not be required when ducts and air treatment systems are located completely within the building's thermal envelope. Once the ducts are installed and before the drywall is installed, a HERS evaluator must visually inspect the duct system to ensure that all duct connections are properly fixed and sealed, preferably with putty.
One may wonder why it is necessary to check ducts for leaks if the ducts and the air controller are located in a conditioned space. The “total leak” test measures the amount of air leaks in all ducts connected to the air conditioning system, including ducts located both outside as well as inside. If the ducts are finally tested for leaks, the HERS evaluator or builder can perform an additional optional duct cleaning test before installing the drywall or use a theatrical smoke machine to detect air leaks and seal them before placing the drywall. Some builders, especially those who install ducts in the attic, prefer to wait until the end to test the ducts, as other trades are likely to move them in the meantime and the ducts will still be accessible.
As required by RESNET standards, the test is performed with a duct tester, such as the Minneapolis Duct Blaster or the Retrotec Duct Tester. For duct leak tests, the standard pressure used is 25 Pascal, which is equivalent to the operating pressure of a typical ducts. If these ducts have loose connections where sections of the duct connect to each other or to the duct covers, trunk lines, or the air controller, air can seep through the cracks. The information provided to check for leaks in ducts in new homes also applies to tests for leaks in ducts in existing homes.
Duct leaks can be a major source of energy loss and comfort problems, and can contribute to humidity problems, especially when ducts pass through an unconditioned space, such as a ventilated attic or mezzanine.