A heat exchange system is provided which transfers the heat from a fluid discharged from a device that utilizes a heated fluid, to fresh fluid in order to increase the temperature of the fresh fluid prior to feeding it into a heating tank. Thus, less energy is required to heat the fluid in the heating tank prior to its introduction into the device which utilizes heated fluid. After the heat has been exchanged, the discharged fluid is then expelled from the system. A fluid trap controls the fluid level in the heat exchanger to assure maximum heat transfer capability. An antisiphon valve is provided in the fresh fluid input of the heat exchange coil in order to prevent discharged fluid from contaminating the fresh fluid source in the event of a rupture in the heat exchance coil. The fluid trap is provided with a pressure activated gate valve which deactivates the fluid trap in the event that the fresh fluid intake pressure decreases below a predetermined level, and thus further prevents contamination of the fresh input fluid by the discharged fluid.