An experimental study is conducted to investigate the effects of a fin pitch and number of tube rows on the air side performance of fin and tube heat exchangers having herringbone wavy fin configuration at various fin thicknesses. A total of 10 samples of fin and tube heat exchanger with a tube outside diameter of 9.53 mm, transverse tube pitch of 25.4 mm and longitudinal tube pitch of 19.05 mm, having various fin pitches, number of tube rows and fin thicknesses, are tested in a well insulated open wind tunnel. The heat exchangers are made from aluminium plate finned, copper tube. Ambient air is used as a working fluid in the air side while hot water is used for the tube side. The results are presented as the variation of the Colburn factor and the friction factor with the Reynolds number based on the fin collar outside diameter (Re-Dc). The experimental results reveal that the fin pitch has an insignificant effect on the heat transfer characteristic. The friction factor increases with increasing fin pitch when Re-Dc. > 2500, approximately. The Colburn factor and the friction factor decrease with increasing number of tube rows when Re-Dc, < 4000, approximately. These results remain the same when the fin thickness is changed. (c) 2004 Elsevier Ltd. All rights reserved.