As an expert in the field of home energy efficiency, I have seen firsthand the impact that duct leakage can have on a home's energy consumption and comfort levels. That's why I always stress the importance of conducting a thorough duct leakage test before and after construction. This simple yet crucial step can make a significant difference in the overall performance of a home's HVAC system. Whether it's done during roughing before drywall construction or after construction, the requirements for a duct test are the same. According to RESNET standards, the system should achieve a leak rate of less than 4 CFM (cubic feet per minute) per 100 square feet of the home.
This means that any leaks in the duct system must be identified and sealed before the home is considered energy efficient. Some builders may choose to wait until the end of construction to test the ducts, especially if they are located in the attic. However, I always recommend testing them as soon as they are installed and before drywall is put up. This allows for any necessary repairs or sealing to be done while the ducts are still easily accessible. Before installing drywall, a HERS evaluator must visually inspect the duct system to ensure that all connections are properly closed and sealed, preferably with putty. If any leaks are found, an optional additional test can be performed using a smoke machine to detect air leaks and seal them before drywall is installed.
This extra step can save time and money in the long run by preventing potential issues with energy loss and moisture problems. The same principles apply when checking for duct leaks in existing homes. The process, known as total duct leak testing, involves creating a negative pressure condition in the duct system and air treatment device (if installed) to measure the amount of air leaks in all connected ducts. Leaky ducts can be a major source of energy loss and comfort problems, especially when they pass through unconditioned spaces like attics or crawl spaces. That's why it's crucial to use a duct tester, such as the Minneapolis Duct Blaster or Retrotec Duct Tester, to accurately measure the amount of leakage in the system. One might question the need for a duct leakage test if the ducts and air treatment device are located within the home's conditioned space. However, I always recommend testing even in these cases, as it allows for any necessary repairs or sealing to be done while it is still easy to access the ducts. The standard pressure used for duct leak tests is 25 pascals, which is close to the operating pressure of a typical duct system.
There are various duct sealing systems available that can effectively fill small openings around duct fittings. It's also important for the evaluator to visually inspect the ducts once they are disassembled to ensure that they are completely isolated and properly insulated. The "total duct leak" test measures the amount of air leaks in all connected ducts, including those located outside and inside the home. This comprehensive approach ensures that all potential sources of leakage are identified and addressed. In some cases, a duct air leak test may not be required if the ducts and air handlers are located entirely within the building's thermal envelope. However, for systems with three or more outlets, a total leak measurement of ≤ 6 CFM25 per 100 m2 is allowed. If any loose connections or cracks are found during the test, it's crucial to seal them properly to prevent air from leaking out.
This simple step can make a significant difference in the overall energy efficiency and comfort of a home.
