Performance testing is a critical component of every HERS® Rating. The procedures for these tests are defined in ANSI/RESNET/ICC 380-2022, which establishes the required methods for equipment setup, measurement, and reporting. Raters and Rating Field Inspectors must perform these procedures carefully and consistently to produce accurate, repeatable test results. Duct leakage testing is one of the three performance tests required by the Standard. It measures the amount of air that escapes from the HVAC duct system during operation. In new construction, duct leakage testing helps verify that the duct system is properly sealed and that conditioned air is delivered to the intended areas of the home. A tight duct system supports energy efficiency, occupant comfort, and indoor air quality. Dwelling Unit and Equipment Setup To prepare the dwelling unit for duct leakage testing, the HVAC system controls must be set to prevent the blower fan from operating during the test (5.2.2). All fans that could affect the pressure of either the Conditioned Space Volume or the space containing the duct system and air handler, such as exhaust fans, must be turned off (5.2.3). Filters must be removed from both the duct system and the air handler cabinet (5.2.5). Supply registers and return grilles must be sealed at both the face and perimeter. If the test is performed before registers or grilles have been installed, the face of each duct boot must be sealed instead (5.2.9). Installing the Duct Leakage Tester There are two approved methods for installing the duct leakage tester. Method 1 involves removing the air handler blower access panel and connecting the duct leakage tester directly to the blower compartment. This method is approved for all duct systems. Method 2 involves installing the duct leakage tester at the largest return grille in the duct system. If multiple return grilles are the same size, the return grille closest to the air handler must be used. This method is permitted only when one of the following conditions applies: The duct system has three or fewer return grilles. Total duct leakage is less than 50 CFM at 25 Pa. Local codes require a license to remove the blower access panel that the Rater or Rating Field Inspector does not possess. The blower access panel is located in an attic or crawl space with limited or restricted access. An example of the fourth condition is an air handler installed in an attic that is accessible only through a pull-down attic stair. Static Pressure Probe Placement The final step in the setup process is installing the static pressure probe(s). Three standard probe locations are approved: A single static pressure probe located at the supply register closest to the air handler (5.3.2.1). A single static pressure probe located in the main supply trunk at least 5 feet from the air handler (5.3.2.2). A single static pressure probe installed in the supply plenum (5.3.2.3). A fourth configuration is required when Method 2 is used and the duct system contains more than three return grilles. In this case, one probe is installed in one of the three approved supply-side locations listed above. A second probe is installed in the return plenum or the return grille closest to the air handler. If the duct leakage tester occupies that location, the second probe is installed at the next closest return grille. The two probes are connected with a tee fitting, and the third leg of the tee fitting is connected to the manometer (5.3.2.4 and 5.3.3). Performing Duct Leakage Testing Once the equipment has been properly installed, testing can begin. Total Duct Leakage For a Total Duct Leakage test, open a door or window to prevent changes in dwelling unit pressure (5.4.1.1). Turn on the duct leakage tester and adjust the fan until the duct system reaches a pressure difference of 25 Pa, within a tolerance of ±3 Pa (5.4.1.2). A recommended procedure is to: Turn on both the duct leakage tester and the manometer. Set the manometer to a 1-second time average. Increase fan speed until the pressure stabilizes near 25 Pa. Change the manometer to a 10-second time average. Once the pressure remains within the allowable tolerance, record the measurement and capture a photograph of the manometer display. Leakage to Outside (LTO) Leakage to Outside (LTO) testing begins with the same equipment setup; however, all exterior doors and windows must remain closed (5.4.2.1). Turn on the blower door and adjust it to create an induced pressure difference of 25 Pa between the dwelling unit and outdoors (5.4.2.2). Once the dwelling unit pressure has stabilized, turn on the duct leakage tester and adjust it until the duct system pressure difference is 0.0 Pa, within a tolerance of ±0.5 Pa (5.4.2.4). After the pressure stabilizes, record the measured airflow as an average over at least a 10-second period (5.4.2.7). As with Total Duct Leakage testing, the most effective approach is to stabilize the equipment using a 1-second time average before switching the manometer to a 10-second averaging period for the final measurement. Conclusion The duct leakage testing procedures in Chapter 5 of ANSI/RESNET/ICC 380-2022 are designed to produce accurate and repeatable results. Proper dwelling unit preparation, correct equipment installation, accurate pressure measurements, and thorough documentation are all essential to obtaining a valid test result. Raters and Rating Field Inspectors with questions regarding ANSI/RESNET/ICC 380 or duct leakage testing should contact their RESNET Accredited Rating Provider. For additional technical assistance, contact the RESNET technical support team at technicalsupport@resnet.us.
