Abstract: Apparatus for a discharge vent on an air circulation system includes structures for controlling the direction and quantity of airflow. Filter elements may be provided to help reduce contaminants that might otherwise be discharged through the vent. Preferred methods for assembling and using the apparatus are disclosed.

Abstract: A pair of elongated channel supports each defining inwardly open channels are secured to the undersurfaces of a parallel pair of ceiling rails. The channel supports are positioned on each side of a ceiling air flow vent. A pair of generally planar control panels are slidably movable within the channels and extend between the channel supports. The panels are movable between alternative positions within the channels to cover all or part of the air flow vent and thereby control air flow therethrough. In an alternate embodiment, the pair of generally planar control panels are replaced by a single larger panel which is similarly movable within the channels of the channel supports.