The invention describes a method and apparatus for controlling the temperature of the floor of a cooking oven by utilizing a recirculating primary heat transfer fluid made to flow through a heat exchanger located in an oven floor. After traveling through the oven floor and absorbing heat, the primary fluid travels to an external liquid-to-liquid heat exchanger wherein the primary fluid transfers heat to a secondary circulating heat transfer fluid. The primary fluid is then recirculated through the oven floor to maintain the floor at a predetermined temperature. The heated secondary fluid may then be utilized for other processes such as in the conveyor belt washing tank of the oven, or it may be discarded. The primary heat transfer fluid may be a thermal oil having a boiling point substantially in excess of 212.degree. F., and having other properties designed to prevent the corrosion, plugging, and fouling of the heat exchanger located in the oven floor. The second fluid is preferably water. The external liquid-to-liquid heat exchanger is easy to clean and service, while the primary fluid avoids degradation of the oven floor heat exchanger. Various sensors may be used to monitor temperature and/or pressure of both the primary and secondary heat transfer fluids as well as other operational allowing a control system to automatically regulate operation of the system.