An environmental control system assembly for an aircraft includes a heat exchanger assembly and a plenum. The heat exchanger assembly includes a first heat exchanger in fluid communication with a source of bleed air, a second heat exchanger disposed adjacent to the first, a third heat exchanger disposed adjacent to the second, and an end sheet. The first heat exchanger includes a first endwall, a first inlet header, a first outlet header, and a first endcap located on the first outlet header. The third heat exchanger includes a third endwall, a third inlet header connected to the third endwall, a third outlet header, and a third endcap located on the third inlet header. The end sheet includes the first, second, and third endwalls. The plenum fluidly connects the first outlet header of the first heat exchanger to the third inlet header of the third heat exchanger.