In this paper, a transient method involving an infrared (IR) set-up is used to investigate local heat transfer distribution over the fin of a staggered elliptical finned tube heat exchanger assembly. An experimental test bench was designed to record data during the fin cooling. The procedure of data preprocessing including IR camera calibration is presented. It allows extracting the temperature field evolution of the fin. These temperatures feed a numerical model that works with thermally thin material and takes into account lateral heat conduction and radiation with the surrounding. The heat transfer coefficient field is determined by integrating the model over time intervals that depend on space. Distributions of Nusselt number over the fin and their uncertainties are presented for several Reynolds numbers. The high resolution of the whole method and set-up allows detecting thermal imprints of developing horseshoe vortices.