exchanger 100 may be any metal known in the art of heat exchanger design in some embodiments the metal components are made from a steel alloy turning now to fig2 a cross sectional view of hot fin structures 104 is shown as shown in fig2 hot fluid enters through hot fluid inlet header 112 and is guided by the hot side fin structures 104 through the heat exchanger hot side first pass 122 and the second pass 124 the flow of hot fluid is redirected at junctions 126 and 128 using a mitered fin to turn the first pass 122 flow 90 u00b0 counter to the cold inlet and then again turn the flow another 90 u00b0 into the second pass 124 as further shown in fig2 a barrier 130 separates the first pass 122 and the second pass 124 the barrier provides a physical separation between the first and second hot fluid passes and contains a void space isolated from the first and second passes of hot fluid passages by u201c void space u201d is meant a space that is void of structure e g an air space in some embodiments the physical separation provided by the barrier 130.