Abstract: A heat exchanger includes a heat exchanger shell having an inlet and outlet. A header plate including an inner member and an outer member defining a leak detection chamber therebetween is provided at each end of the heat exchanger shell. A plurality of heat exchanger tubes is positioned in the heat exchanger shell. Each tube extends through an aperture formed in an inner member and an aperture formed in an outer member of each of the header plates. A seal is provided in a channel in each aperture to sealingly engage a corresponding heat exchanger tube and a corresponding plate. A passage leads from the leak detection chamber to the exterior of the header plate.