A multiple-pass heat exchanger having opposing headers with beveled end walls, one header having nozzles on opposite sides of a separator wall for delivering heat exchange fluid at one temperature from one or more nozzles on one side of the separator wall, the heat exchanger having one set of fluid flow tubes for conveying the fluid in one direction to the other header and another set of fluid flow tubes for carrying the fluid in the opposite direction from the latter header for delivering to the header with a nozzle or nozzles for discharging the fluid from the latter header at a changed temperature. There is also disclosed a multiple systems combined heat exchanger having an opposing headers with beveled end walls, wherein at least two heat exchangers independent of each other share the respective headers which are divided from each other by separator walls.