Abstract: A variable air filter system is described for convection and ventilation air flows, filter elements being introduced into the air flow in order to clean or purify the room air. To obtain an improved filtering effect, provision is made for filter elements to be disposed at a distance in front of or above the air-generating surface or the air-generating cross-section, the area of such filter elements being as large as or, if required, larger than the air-generating cross-section of the air-emitting surface. It is possible to provide the filter elements with the facility of enabling different inclination, form, overall depth, and length and height arrangement to be adjusted to the optimum value for filter efficiency in the air flow for cleaning.