The dynamic responses of the temperatures of the outlet water and the wall for a vertical tube heat exchanger, were studied as a function of the sinusoidal change in the inlet water temperature. The experimental response data for the outlet water temperature were compared with the calculated data from the derived equation. The comparison was shown to be in good agreement between the experiment and thr throry in the present range of the experiment. The inlet water-to-wall temperature transfer function was derived, and the theoretical frequency response characteristics were compared with the experimental data. The experimental data were lower than those predicted from the theory.