A system for rapidly raising the temperature of a product having low thermal conductivity from a cold to a heated state in a manner bringing the internal temperature of the entire body of the product to substantially the same predetermined elevated temperature level. The system includes a chamber having a fluid-permeable product receiving section flanked by input and output plenums, and a main flow loop in which the chamber is connected in a continuous flow path in series with a heater station and an air pump in an arrangement in which air drawn from the output plenum and creating a negative pressure therein is conducted through the heater station and then forced in the heated state through an input line leading into the input plenum to create a positive pressure therein. The resultant pressure differential between plenums causes heated air to flow at high velocity through the section to heat the product therein. A bypass extending between the input to the heater station and the junction of the chamber and the pump in the main flow loop defines a feedback flow loop which excludes the chamber. A damper mechanism at this junction is cyclically operated to periodically block the flow of heated air into the chamber and to divert the flow into the bypass of the feedback loop for recirculating therein. As a consequence, main-loop flow through the chamber assumes the form of a pulsatory wave whose fluidic pulses have a peak temperature well above the predetermined level and whose relaxation periods are at a temperature below the predetermined level to promote rapid heat transfer in the body without, however, raising the surface temperature thereof above this level, the action continuing until the entire body of the product is at the desired level.