This study presents the effect of an inclination angle from the vertical position on the air-side thermal hydraulic performance for a multi-louvered fin and flat tube heat exchanger. For a heat exchanger with a louver angle of 27 degrees, fin pitch of 1.4 mm and flow depth of 20 mm, a series of tests for dry and wet surface conditions were conducted for the air-side Reynolds numbers of 100-300. The inclination angles from the vertical position were 0 degrees, +/-30 degrees, +/-45 degrees, and +/-60 degrees clockwise. The heat transfer performance for both dry and wet conditions was neither influenced significantly by the inclination angle (-60 degrees < <theta> < 60<degrees>), nor by the presence or absence of an upstream duct, while the pressure drops increased consistently with the inclination angle. The heat transfer coefficients and the pressure drops for the wet conditions revealed the importance of the role of condensate drainage. (C) 2001 Published by Elsevier Science Ltd.