Abstract: A heat transfer fluid is used in a heating apparatus including, in series, a fluid storage container including conventional primary heating system for bulk heating the heat transfer fluid to a preselected temperature, and a secondary heating system utilizing an ultra-violet ray system for preheating the heat transfer fluid after it is cooled in a heat exchange system, but before it is returned to the fluid storage container. A connecting system is provided for transporting the heated fluid in series from the storage container, to the heat exchange system, to the ultra-violet ray heating system, and then back to the storage container. In operation, the fluid is heated in the storage container, and is then cooled as it passes through the heat exchange system. The cooled fluid is then preheated by the ultra-violet light ray heating system prior to its return to the storage container for further heating.