A ventilation device, intended to equip a livestock building (90, 91), comprising a casing and at least one heat exchanger block, the casing being provided with an exterior air intake, a heated air outlet, an interior air intake and a cooled air outlet, said at least one heat exchanger block being able to thermally contact a first flow of air coming from the exterior air intake, and directed towards the heated air outlet, with a second flow of air coming from said interior air intake, the ventilation device further comprising an additional air outlet disposed on said casing, air heating means and deflection means capable of directing said second flow of air entering at the location of said interior air intake: - through said at least one exchanger block towards said cooled air outlet according to a first air circuit (Cl), - through a passage towards the heating means and said heated air outlet according to a second air circuit, or - directly towards said additional air outlet according to a third air circuit, said deflection means comprising: - a first flap movable between a closed position and an open position of said exterior air intake, - a second flap movable between a closed position and an open position of said additional air outlet, and - a third flap movable between a closed position and an open position of the passage between said interior air intake and said heated air outlet. said at least one heat exchanger block being able to thermally contact a first flow of air coming from the exterior air intake, and directed towards the heated air outlet, with a second flow of air coming from said interior air intake, the ventilation device further comprising an additional air outlet disposed on said casing, air heating means and deflection means capable of directing said second flow of air entering at the location of said interior air intake: - through said at least one exchanger block towards said cooled air outlet according to a first air circuit (Cl), - through a passage towards the heating means and said heated air outlet according to a second air circuit, or - directly towards said additional air outlet according to a third air circuit, - through said at least one exchanger block towards said cooled air outlet according to a first air circuit (Cl), - through a passage towards the heating means and said heated air outlet according to a second air circuit, or - directly towards said additional air outlet according to a third air circuit, said deflection means comprising: - a first flap movable between a closed position and an open position of said exterior air intake, - a second flap movable between a closed position and an open position of said additional air outlet, and - a third flap movable between a closed position and an open position of the passage between said interior air intake and said heated air outlet. - a first flap movable between a closed position and an open position of said exterior air intake, - a second flap movable between a closed position and an open position of said additional air outlet, and - a third flap movable between a closed position and an open position of the passage between said interior air intake and said heated air outlet.