The effect of inclination angle on the louver finned tube heat exchanger subject to natural convection condition is reported in this study. It is found that the inclination angle plays an importance role on the performance of the louver finned heat exchanger. Performance of the beat exchanger is associated with the interactions between fin, louver, tube, and inclination angle. The heat transfer performance generally decreases with the rise of the inclination angle. This decrease of heat transfer performance is due to the blockage fin and its reversed heat dissipating direction against the raising air. However, at an inclination angle such as 30-45 degrees, a considerable increase of heat transfer performance is seen. This is because appreciable amount of air flow was directed by the louver, causing a "louver-directed" phenomenon as that of in forced convection. With a further increase of inclination angle, the blockage effect caused by the fin is so strong as to offset the "louver-directed" phenomenon. Unlike those shown in force convection, the heat transfer performance decreased with the number of tube row. (c) 2006 Elsevier Ltd. All rights reserved.