In an experimental investigation temperature fields and mean heat transfer coefficients were obtained on a finned tube. The diameter of the fin was varied in order to find out about the effect of fin height. Such an effect on the heat transfer coefficient vanishes in a correlation given in the literature. By thermovision the usefulness of the fins can be observed : the smaller fin proved to be better than the larger one under given conditions. The heat transfer coefficient depends on fin height, with better heat transfer for smaller fins. The respective correlation based on thermovisually obtained fin temperatures is presented. For the more practical case, with the Grashof number being based on the temperature difference between central tube and ambient air, an improved correlation is presented with less than 6% scatter.