A portable unit for heating packages containing pre-cooked cold food, the unit acting to rapidly heat up the food to a service temperature level and to thereafter maintain this level. The unit includes a case having a rack therein divided by shelves into a series of compartments, each adapted to receive a food package. Standing vertically behind the rack is an air modulator including a stationary outer tube having a series of longitudinally-aligned ports communicating with the respective compartments. Rotating within the outer tube is an inner tube having a series of angularly-displaced holes which successively register with the ports in the course of a rotary cycle. Air drawn from the free region in the front of the rack is conveyed through a heater station and from there blown into the inner tube to create a pressure differential between the free region and the inner tube. As a consequence, the heated air is projected successively through the ports into the compartments whereby the heated air flowing at high velocity through each compartment has a pulsatory waveform which acts to rapidly heat the food therein.