Operable blade louvers protect air intake and exhaust openings in exterior walls. The design allows blades to be open or closed and are most often supplied with factory mounted and adjusted electric actuators. When in the open position these louvers function as a conventional louver. When in the closed position they provide a tight shutoff from air and other elements. These louvers provide good protection against rain infiltration under ambient conditions but lend little protection against wind driven rain when in the open position.