The paper presents results of laboratory-measured performance of fan-filter units (FFUs) used for cleanrooms. A total of twenty FFUs collected from the market were tested, including thirteen 1220 mm x 610 mm (or 4 ft x 2 ft) units and seven 1220 mm x 1220 mm (or 4 ft x 4 ft) units. The paper concludes that there are wide variations in FFUs energy performance, and that there are opportunities in improving energy efficiency and lowering operating costs of FFUs. Furthermore, the paper suggests the benefits of having a uniform method for testing and reporting FFU performance. Such a testing method and recommended practice guideline is under development, with heavy input from FFU suppliers, users, and independent institutions that include Lawrence Berkeley National Laboratory (LBNL), Industrial Technology Research Institute (ITRI), and Institute of Environmental Sciences and Technology (IEST). An integrated approach with the participation from designers, suppliers, users, and utility companies can help to identify energy-efficient FFUs that are required for many cleanroom applications.