A fuel cell stack end unit, comprising: an assembly adapted to receive first and second gases, to convey said first and second gases in heat exchange relationship and to output said gases after heat is transferred from one gas to another, said assembly comprises: a first unit for defining an enclosed gas flow path for said first gas; and a second unit enclosing said first unit and defining a gas flow path for said second gas intersecting said first unit, wherein said first and second units (2A, 2B) act as a heat exchanger adapted to transfer heat from said second gas to said first gas, said first unit includes a plurality of tubes (19A, 19B) for receiving and carrying said first gas and said second unit comprises an enclosure in which said plurality of tubes (19A, 19B) are disposed, said plurality of tubes (19A, 19B) has a surface area adapted to transfer heat from said second gas flowing in said second unit to said first gas flowing in said tubes (19A, 19B), said second unit is in the form of a hollow box forming said enclosure, said hollow box defining exterior walls (14, 15A, 15B, 16, 25A, 25B) of said heat exchanger, wherein said hollow box comprises an inlet port and an outlet port, said second gas flows into said second unit through said inlet port and flows out of said second unit through said outlet port, and wherein said second gas flows through said second unit in a direction transverse to the direction of said plurality of tubes (19A, 19B) in said first unit, characterized in that said hollow box has first and second opposing exterior walls (15A, 15B) and said inlet port is disposed in said first exterior wall of said hollow box and said outlet port is disposed in said second exterior wall of said hollow box, and wherein said first unit further comprises an inlet chamber and an outlet chamber, said outlet chamber being connected to said inlet chamber by said plurality of tubes (19A, 19B). an assembly adapted to receive first and second gases, to convey said first and second gases in heat exchange relationship and to output said gases after heat is transferred from one gas to another, said assembly comprises: a first unit for defining an enclosed gas flow path for said first gas; and a second unit enclosing said first unit and defining a gas flow path for said second gas intersecting said first unit, wherein said first and second units (2A, 2B) act as a heat exchanger adapted to transfer heat from said second gas to said first gas, said first unit includes a plurality of tubes (19A, 19B) for receiving and carrying said first gas and said second unit comprises an enclosure in which said plurality of tubes (19A, 19B) are disposed, said plurality of tubes (19A, 19B) has a surface area adapted to transfer heat from said second gas flowing in said second unit to said first gas flowing in said tubes (19A, 19B), said second unit is in the form of a hollow box forming said enclosure, said hollow box defining exterior walls (14, 15A, 15B, 16, 25A, 25B) of said heat exchanger, wherein said hollow box comprises an inlet port and an outlet port, said second gas flows into said second unit through said inlet port and flows out of said second unit through said outlet port, and wherein said second gas flows through said second unit in a direction transverse to the direction of said plurality of tubes (19A, 19B) in said first unit, characterized in that said hollow box has first and second opposing exterior walls (15A, 15B) and said inlet port is disposed in said first exterior wall of said hollow box and said outlet port is disposed in said second exterior wall of said hollow box, and wherein said first unit further comprises an inlet chamber and an outlet chamber, said outlet chamber being connected to said inlet chamber by said plurality of tubes (19A, 19B).