The Interceptor HEPA filter can be set up to process air that is going into or coming out from beneath cabinets, walls, ceilings and floors. It is important to know that HEPA filters do not make a HEPA system. Only by processing all air negatively, can a HEPA system be achieved. All air is processed before going through the blower in either negative or positive drying modes thus never contaminating equipment. Extend the life of your HEPA system by replacing the pre-filter (green and yellow) often.