In this work, a novel built-in-storage type solar water heater of about 871 capacity has been investigated theoretically and experimentally for the case of no draw-off. The solar water heater which performs the dual function of absorbing and storing hot water is made of 5 pipes, each of length 1.8 m and diameter 12 cm. A baffle plate is placed inside each pipe. The experiments have been performed inside the laboratory using an artificial Sun consisting of 27 lamps. The water temperatures have been measured at various locations in the system. In the theoretical study, transient performance of the system is predicted by solving the mathematical model consisting of energy balance equations written for each control volume comprising one length of pipe. These equations are converted to finite difference form and then solved by a personal computer. The experimental results have been compared with the numerical model and a good agreement has been found between the experimental results and the theoretical predictions. Copyright (C) 1997 Elsevier Science Ltd.