A ventilation device , intended to equip a livestock building , 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 (A) of air coming from the exterior air intake , and directed towards the heated air outlet , with a second flow (B) 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 (B) 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 (C2), or - directly towards said additional air outlet according to a third air circuit (C3), 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 (A) of air coming from the exterior air intake , and directed towards the heated air outlet , with a second flow (B) 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 (B) 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 (C2), or - directly towards said additional air outlet according to a third air circuit (C3), - 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 (C2), or - directly towards said additional air outlet according to a third air circuit (C3), 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 . <EOS>