Abstract: An exhaust gas heat exchanger has a tube which is made of a stainless steel and in which exhaust gas flows, and an inner fin which is made of a stainless steel and arranged in the tube to improve a heat exchange between the exhaust gas and cooling water. The cooling water flows at an outer side of the tube. The fin pitch fp of the inner fin is substantially in the range of 2 mm<fp?12 mm, and the fin height fh of the inner fin is substantially in the range of 3.5 mm<fh?12 mm.

Abstract: A heat exchanger has tubes defining first fluid passages through which a first fluid flows therein, an inlet part and an outlet part. Each tube has a first main wall and a second main wall. At least one of the first main wall and the second main wall has a projection projecting outside of the tube along a peripheral end and a first recess and a second recess recessed from the projection. The tubes are stacked such that the first and second main walls are opposed to each other and spaces are provided between the adjacent tubes by the projections. The spaces define second fluid passages through which a second fluid flows. The inlet part is in communication with the second fluid passages through the first recesses and the outlet part is in communication with the second fluid passages through the second recesses.