Abstract: A heat exchanger assembly comprising a stacked array of heat exchange channel elements, having first fluid entrance and exit faces at opposite ends of the array. The improved headering arrangement includes sealing members each having a bearing surface with a generally corrugated contour which is bonded to the correspondingly contoured edge walls of the channel elements along a side of the stacked array and header tank means joined to the sealing members so as to leak-tightly enclose the associated face of the stacked array of heat exchange channel elements.