The present invention concerns a device for heating wrapped batches of products and a packaging installation provided with such a heating device, specifically comprising a manifold of heating means with lines of orifices and a means for blocking the orifices using a mobile plate comprising for each line of orifices openings, at least two successive openings having different lengths, to go 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 maintaining open said second line of orifices, and vice-versa.