Heat transfer performance of four heat exchanger specimens are experimentally investigated. Each of these four are geometrically identical with the exception of fin shape and whether the 1 st and 2nd rows are connected or separated. The diameter, number of row and fin spacing of the heat exchangers examined in the present work are 7 mm, 2 rows and 18 fpi, respectively. Two fin shapes, slit and louver, are tested. For the same fin shape, two heat exchanger specimens are examined. One is such as fins in each row are separated. The other one's fins are physically connected with each other so that the fin width doubles and they accommodate two rows. The experiments were carried out using psychrometric calorimeter, which is based on air-enthalpy method described in ASHRAE standards. During experiments for air-side heat transfer coefficient measurements in each row, tube-side water flow rate is controlled to maintain the temperature difference of water in each row at 5 °C. Frontal air velocity are varied from 0.7 m/s to 2.5 m/s. Heat transfer coefficient in terms of Colburn j-factor are presented. The results show that conduction through fins influence air-side heat transfer coefficient in each row.