Abstract: A rotary heat exchanger for heat exchange between at least two gaseous media comprises an annular heat transfer member rotating in a housing. A stationary partitioning wall is provided within the heat transfer member, thereby defining therein first and second semicircular chambers communicating with inlet openings in the housing. Outlet diffuser chambers are provided outside the heat transfer member and increase in width towards their outlet ends for the discharge from the apparatus. The partitioning wall is provided with a screening wall portion at at least one edge adjoining the inside surface of heat transfer member. The partitioning wall may be of a heat-insulating construction, while the heat exchanger may be combined with a fan assembly disposed in parallel relationship with the heat exchanger so the arrangement can be operated in a heat exchange mode or a pure fan blowing mode, being controllable by flow control flaps.