This paper systematically explores the heating effects in a Hartmann whistle. Effects of thermal losses on the end-wall heating of the whistle are demonstrated by conducting experiments on bare metal cavities, insulated metal cavities, and in wooden cavities. The heating studies are done on wooden cavities of three different configurations, namely, regular cylindrical, stepped and conical ones. The cavity with conical geometry is observed to provide the maximum heating effect at the end-wall. Further, the effects of various parameters such as nozzle pressure ratio, cavity length, and stand-off distance on the end-wall heating of the cavities are also studied. The relationship between acoustic resonance and heating effects are established.