A ventilating apparatus for mounting in a roof and comprising a central shaft for exhausting spent air from the ventilated room, a surrounding annular duct divided in an upper and a lower section by means of a transverse partition wall secured to the periphery of an exhaust blower wheel located in the central shaft. Separate blower vanes are secured to the upper and lower face of the partition wall for delivering fresh air from the ambient and recirculated air from the room, respectively, to a mixing chamber surrounding the annular duct and opening into the room. Individually adjustable valve means are provided in the inlet openings from the upper and lower duct sections to the mixing chamber.
