What is a good duct leakage test?

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. There are many duct sealing systems available that will fill most small openings around duct fittings. As required by RESNET standards, the test is performed with a duct tester, such as the Minneapolis Duct Blaster or the Retrotec Duct Tester.

Footnote 40) In the case of a duct system with three or more returns, the total leak measured by the Rater is allowed to be equal to or greater than ≤ 6 CFM25 per 100 square meters. 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. One application, known as a total duct leak test, creates a negative pressure condition in the duct system and in the air controller, if installed. Leaky ducts can be a major source of energy loss and comfort problems, and they can contribute to humidity problems, especially when the ducts pass through an unconditioned space, such as a ventilated attic or mezzanine. 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 and inside. Some builders, especially those who install ducts in the attic, prefer to wait until the last test to check the ducts, since, in the meantime, other operators are likely to move them and the ducts will remain accessible. 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. There will be no need to test air leaks in ducts when ducts and air treatment systems are fully located within the building's thermal envelope.

In addition, the evaluator must visually check, when entering, that the ducts are completely insulated (R-8 for supply ducts and R-6 for return ducts and other ducts) along their length, including all connections, and that the insulation is not compressed by tight belts, structural elements or excessive bending. Some builders prefer to check the ducts for leaks when entering, when they are easier to access, in case it is necessary to additionally seal the air. 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. If these ducts have loose connections in which some sections of the duct connect to each other or to duct junctions, trunk lines, or the air treatment system, air can seep through the cracks.

When all ducts are located in conditioned spaces, it is only necessary to perform the total duct leak test if certain conditions are met.

Estelle Bookhart
Estelle Bookhart

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