Abstract: An air flow filter assembly of the side-loading type includes a filter guide track adjacent a side access opening for supporting multiple air filter elements in an operative position across the air flow passage. An internal closed loop seal assembly provides an effective, independent peripheral seal for each track-mounted filter element. A gasket retainer, mounted within the air flow passage adjacent the filter track, includes frame segments forming a rectangular gasket frame bordering one or more air flow windows or cells. A seal gasket is mounted on each gasket frame, with each seal gasket including a resilient flange portion extending in a closed loop around each air flow window or cell. The closed loop flange portion projects from the gasket frame for engaging and resiliently sealing along the face of a filter element supported on the filter track in air flow alignment with the air flow window or cell.