Duct Leakage Testing2019-01-21T04:44:21+00:00

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Just as important as the proper installation of an HVAC system are the troubleshooting and maintenance. HVAC systems, like any component, can sustain wear or damage over time and should be maintained with regularity in order to ensure optimal efficiency. Ducts are especially important to check, since their wall- or ceiling-mounted positioning makes it important that they are made of relatively light materials. This means they can be more vulnerable to damage than some other building components. A technician, such as our qualified technicians here at HVAC Engineering, can help recommend any needed maintenance after performing some tests to check the performance of your system.

Duct leakage testing is a method that allows for the measurement of air leaks in an HVAC system, which can be responsible for losses of temperature-controlled air. Since it takes valuable energy to heat and cool air to a comfortable temperature, duct leakage testing can help reduce energy waste and save on recurring costs. Counter-intuitively, duct leakage testing can involve not just a duct leakage tester, but other key equipment such as a blower door or a flow hood. The method is relatively straightforward: “[j]ust as when you’re testing for airtightness, each cubic foot of air that leaks out (of the duct system in this case) must be made up by a cubic foot of air blown in by the fan”.1 What this means is that we’re able to test an HVAC system by measuring the flow of air entering and leaving the system, and the difference between the two readings indicates the magnitude of leakage within the ducts. As in any good experiment, however, it is important to control for other variables, such as the pressure already present in the HVAC system. For this reason, duct leakage testing is often preceded by a pressurization of the system using a fan with a known flowrate, so that any flexure of the duct walls is not erroneously included in the leakage reading.

However, duct leakage testing is not entirely this simple. As stated in “Duct Leakage Testing, Basic Procedure”, it’s important to make the distinction between leaks that are truly wasting valuable energy- dubbed “malignant” leaks- and those which are more “benign”. For a leak to be causing a total loss of conditioned air, it must be leaking to an area outside the building envelope. In order to test for malignant leaks alone, benign leaks must be controlled. This can be achieved by pressurizing the duct system and the interior of the building envelope to the same level, thereby eliminating the pressure imbalance that causes air to leak out of the duct system and into the lower-pressure building interior. As you might remember if you’ve taken a Physics class, gases naturally move from areas of higher pressure to areas of lower pressure if given a channel between the two. Once the equal pressurization is achieved, gases will only have a pressure differential between inside the building envelope and outside of it- thereby making it possible to separate out which leaks are malignant. Once the duct leakage testing has been completed, the results can be analyzed to help optimize your HVAC system to its best performance.

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