This is an invaluable aid in the effective understanding of heat exchangers. The hot water unit comprises of a tank fitted with electrical immersion heaters. It has a facility to circulate hot and cold water through flow meters with the help of motor driven pumps. Shell and tube heat exchanger and/or a concentric pipe heat exchanger and/or plate type heat exchanger is provided to conduct the experiment. Other type of heat exchangers can be provided, on request. The system facilitates the study of parallel and counter flow as well.