This document describes a procedure for measuring the performance of general ventilation air cleaning devices in their end use installed configuration. The performance measurements include removal efficiency by particle size and the resistance to airflow. The test procedures include the definition and reporting of the system airflow.The procedure describes a method of counting ambient air particles of 0,3 µm to 5,0 µm upstream and downstream of the in-place air cleaner(s) in a functioning air handling system. The procedure describes the reduction of particle counter data to calculate removal efficiency by particle size.Since filter installations vary dramatically in design and shape, a protocol for evaluating the suitability of a site for filter evaluation and for system evaluation is included. When the evaluated site conditions meet the minimum criteria established for system evaluation, the performance evaluation of the system can also be performed according to this procedure.This document also describes performance specifications for the testing equipment and defines procedures for calculating and reporting the results. This document is not intended for measuring performance of portable or movable room air cleaners or for evaluation of filter installations with an expected filtration efficiency at or above 99 % or at or below 30 % when measured at 0,4 µm.