A louver-finned flat tube heat exchanger was tested, and the data are compared with those of the state-of-the-art round tube heat exchanger. Both heat exchangers have the same tube perimeter and fin pitch. Tests were conducted under dry and wet condition. Results show that, under dry condition, both j and f factors of the round tube heat exchanger are larger than those of the flat tube heat exchanger. As the Reynolds number decreases, however, the j and f factors of the flat tube heat exchanger increase at steeper slopes than those of the round tube heat exchanger. Under wet condition, contrary to the dry surface, both j and f factors of the flat tube heat exchanger are larger than those of the round tube heat exchanger. Explanation is provided considering the condensate drainage between louvers and fins. Performance evaluation was also performed.