Device for heating wrapped batches of products, comprising at least: - an oven provided with at least one section; - at least one conveyor for said wrapped products passing through said at least one section; - means for heating said at least one section; - the heating means comprising at least one heating unit, at least one circuit connecting said heating unit and discharging inside said at least one section, and at least one means for causing a flow of air heated by said heating unit to circulate towards said circuit; - for each section, each heating means comprising at least one manifold connected at the outlet of at least said circuit, each manifold extending along at least a part of said corresponding section; - said at least one manifold comprising at least one wall provided with orifices of equivalent sizes, said orifices being distributed in lines on the surface of said wall, the horizontally extending lines of orifices forming rows, the vertically extending lines of orifices forming columns, the adjacent orifices of one and the same line being spaced apart by at least one determined centre-to-centre spacing; - at least one means for blocking the orifices of at least two lines comprising at least one plate that is able to be moved in at least one direction of movement relative to said wall of said manifold, said plate comprising, for each line of orifices, openings spaced apart by an interval, each opening having a length at least equivalent to the size of an orifice; characterized in that - at least two successive openings have different lengths, to go in said direction of movement a) from a position blocking at least a first line of orifices and opening at least a second line of orifices, b) to another position opening said first line of orifices whilst keeping said second line of orifices open, and vice versa. - an oven provided with at least one section; - at least one conveyor for said wrapped products passing through said at least one section; - means for heating said at least one section; - the heating means comprising at least one heating unit, at least one circuit connecting said heating unit and discharging inside said at least one section, and at least one means for causing a flow of air heated by said heating unit to circulate towards said circuit; - for each section, each heating means comprising at least one manifold connected at the outlet of at least said circuit, each manifold extending along at least a part of said corresponding section; - said at least one manifold comprising at least one wall provided with orifices of equivalent sizes, said orifices being distributed in lines on the surface of said wall, the horizontally extending lines of orifices forming rows, the vertically extending lines of orifices forming columns, the adjacent orifices of one and the same line being spaced apart by at least one determined centre-to-centre spacing; - at least one means for blocking the orifices of at least two lines comprising at least one plate that is able to be moved in at least one direction of movement relative to said wall of said manifold, said plate comprising, for each line of orifices, openings spaced apart by an interval, each opening having a length at least equivalent to the size of an orifice; characterized in that - at least two successive openings have different lengths, to go in said direction of movement a) from a position blocking at least a first line of orifices and opening at least a second line of orifices, b) to another position opening said first line of orifices whilst keeping said second line of orifices open, and vice versa. a) from a position blocking at least a first line of orifices and opening at least a second line of orifices, b) to another position opening said first line of orifices whilst keeping said second line of orifices open,