Abstract: The invention relates to an improved fin and tube type heat exchanger wherein thin, heat-conducting fins act as a secondary heat-exchange surface for a heat-conducting medium flowing through the tubes. The thin fin plates substantially lie in a plane perpendicular to the air flow and have angled louvers formed therein. The angled louvers have a short leg and a long leg, with the short leg preferably in the fin plane with the long leg bent therefrom. The unequal length legs permit a larger condensate gap between the trailing edge of one louver and the leading edge of the next louver. With the combination of an angled louver plus the short leg lying in the fin plane, a substantially strong fin is provided even with a thin fin plate. The combination of the short leg lying in the direction of air flow, with the longer leg being inclined thereto, allows a high heat transfer coefficient at the leading edge, while the angled portion behind the leading edge generates a turbulent flow to reduce boundary layer growth.