A duct leak test, also known as a duct test, is a procedure that can be conducted before drywall is installed or after construction. The requirements for the test are the same regardless of when it is performed. Five days prior to the test, the system must achieve a leak rate of less than 4 CFM (cubic feet per minute) per 100 square feet of the home. Before the drywall is installed, a HERS evaluator must visually inspect the duct system to ensure that all connections are securely closed and sealed, preferably with putty.
An optional duct cleaning test can be performed before the drywall is installed, or a theatrical smoke machine can be used to detect air leaks and seal them before the drywall is put in place. In the case of a duct system with three or more return points, the total leak measured by the Rater must be equal to or less than 6 CFM25 per 100 square meters. The same rules apply when testing for leaks in existing homes, as long as all ducts are located in conditioned spaces. The total duct leak test creates a negative pressure condition in the duct system and in the air controller, if one is installed.
The HERS evaluator must also visually check that all 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 tight belts, structural elements, or excessive flexion. Some builders prefer to wait until after construction to test for leaks, as other trades may move the ducts in the meantime and they will still be accessible. On the other hand, some builders prefer to check for leaks when entering, as they are easier to access at this point. A duct air leak test will not be required when all ducts and air treatment systems are located within the building's thermal envelope.
The “total leak” test measures the amount of air leaks in all connected ducts, including those located both outside and inside. If leaks are tested at entry, a HERS evaluator must confirm and document that the total leak in the ducts is less than 4 CFM 25 per 100 square feet of conditioned floor area or 40 CFM25 using an approved test protocol from Resnet. The evaluator must also verify through visual inspection that all duct covers are sealed to finish surfaces at the end. Leaky ducts can be a major source of energy loss and comfort problems, and they can contribute to humidity issues when they pass through an unconditioned space such as an attic or mezzanine.
There are many sealing systems available that can fill most small openings around fittings. It may seem unnecessary to test for leaks if all ducts and air controllers are located in conditioned spaces; however, it is important to remember that even small leaks can add up over time and lead to significant energy losses. A good duct leakage test should be conducted by a certified HERS evaluator who has experience with this type of testing. The evaluator should use an approved testing protocol from Resnet to ensure accuracy and reliability of results.
The evaluator should also visually inspect all connections and seals to ensure that they are secure and properly sealed with putty or other sealant material. Additionally, they should check that all insulation is properly installed along its entire length without any compression from tight belts or structural elements.