Heat exchanger

In a cross finned tube heat exchanger including a multiplicity of side-by-side fin plates, and a plurality of heat transfer tubes extending through the fin plates at least in one row to provide a serpentine flow passage for a heat transfer medium which exchanges heat with another heat transfer medium flowing across the surfaces of the fin plates, a multiplicity of stepped louvers are formed on the wall of each fin plate between the adjacent heat transfer tubes of the same row. The stepped louvers each extending in a direction at right angles to the direction of air flow across the surfaces of the fin plates include at least one tilting rise wall and may differ from one another in shape depending on their positions. The stepped louvers on each fin plate may be arranged in the form of waves or uniform in height with respect to the direction in which each fin plate extends. The adjacent stepped louvers have edges varying in vertical positions.