This work continues the study of heat transfer and pressure drop performance of integral inner fin tubes, designed to enhance the heat transfer performance of smooth tubes for use in high performance compact heat exchangers. A previous paper described the performance of integral inner fin tubes for heating water in turbulent flow. In this paper, performance data for heating air in turbulent flow are presented for the same tubes, manufactured by the French Tube Division, Noranda Metal Industries, Newtown, Connecticut, under the name Forge-Fin(TM). Eighteen different inner fin copper tubes with smooth outside surfaces were employed, 5 with straight fins and 13 with spiral fins. A commercial smooth copper tube was tested for comparison. Tube dimensions are given in Table 1, and the cross-sections are shown in Fig. 1. For ease of discussion, the spiral fin tubes were divided into low spiral with the fin height/inside diameter ratio less than 0.05 and into high spiral with the ratio greater than 0.065.