a filter frame is removably attachable to a box fan . the filter frame is adapted for receiving a standard hvac - style filter for removing contaminants from air flow induced by the fan . in this manner , a cost - effective means for filtering a flow of air is provided for residential and commercial settings . the filter frame is adaptable to a variety of standard box fan types of different styles and dimensions . the frame is configured to accommodate standard filters , such as those readily available from retail hardware stores and home centers .