ASHRAE Standard 120 establishes uniform methods of laboratory testing of HVAC ducts and fittings to determine their resistance to airflow. The fitting losses, which are reported as local loss coefficients, are used to update and refine the ASHRAE Duct Fitting Database. To date, at least six research projects have used the test methods of Standard 120 to improve this database.
The 2008 revision of the standard was undertaken primarily to correct some errors in the original edition of the standard and to clarify its language in places.

This standard may be used to determine the change in total pressure resulting from airflow in HVAC ducts and fittings. The test results can be used to determine duct flow losses in pressure loss per unit length. Fitting losses are reported as local loss coefficients. This standard does not cover interpretation of test data.

Keywords: duct design, duct flow resistance, duct performance, HVAC duct efficiency, testing ducts, hvac duct tests