The invention is directed to a heat exchange module to help employ usable heat to pre-warm a water supply prior to entry into a tankless water heater. The module comprises an insulated housing having an inner shell having a top end, bottom end and cylindrical middle portion. A first intake attaches to the insulated housing which introduces cooling water from the cogeneration system, while a second intake feeds the water supply coils (positioned within the insulated housing) to effectuate heat exchange with the cooling water. After heat exchange, a first outlet removes cooling water for return to the cogeneration system, while a second outlet removes the water supply from the cooling coils. Upon removal, this water supply may be fed into a tankless water heater. A controller connected to both outlets and inlets optimizes efficient exchange of energy through timing introduction and removal of the water supply from the module.