Filtered Air System for 1" grid (#4877) Four-way airflow. Reduces cold and hot spots while creating a more uniform ambient temperature throughout the room. Filters air as it exits the ceiling diffuser and stops dust from collecting on ceiling tiles. Includes 2 sets of 3-ply dust trapping filters. Change filters approx. every 6 months. Installs easily to existing ceiling grid using 4 heavy duty, preinstalled magnets.