An air valve includes a frame and a sheet of thin material. The frame may have an outlet-side member configured mounted on a fan housing and an inlet-side member rotatably coupled to the outlet-side member. The material may have top and bottom edges, and a plurality of folds perpendicular to the top and bottom side edges that divide the sheet into a plurality of sections. The material may be attached to the outlet-side member and the inlet-side member, and configurable between folded and expanded positions. An attraction between a magnetic component on the inlet-side member and a magnetic component on a rotating fan blade may cause the inlet-side member to rotate, moving the material into the folded configuration. When the fan blade is not rotating, a spring attached at a pivot point may cause the inlet-side member to rotate in an opposite direction, moving the material into the expanded position.