An apparatus for feeding/heat sealing cartons along the feed path of a cartoning line is provided. A conveyor moves the cartons past the heat sealing station where an elongated nozzle assembly forms a heated air stream directed against the carton flap and the side of the carton to activate the coating to form an adhesive. A bypass valve and duct is provided to interrupt the flow of heated air in the event that the carton does not clear the activation zone in a predetermined time. Strategically placed heat shields and coolant passages are provided to further isolate the conveyor from the heat. The nozzle includes a slotted outlet with an elongated bar closely spaced above to deflect the heated air stream when a carton is present for adhesive activation; said bar having a tapered fin to form a modified air foil along the trailing edge to divide, recombine and compact the stream when a carton is not present. The upper feed belts of the conveyor are adjustable to adapt to cartons of various heights.