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.