A counter-top 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 an apertured partition therein to form a compartment accessible from the front of the case for accommodating a stack of food packages with air-flow spaces therebetween. The compartment is spaced from the rear of the case to define a plenum and from the front to define an air curtain passage communicating with upper and lower air passages leading to the plenum. In operation, air drawn from the upper passage is heated and blown into the plenum to create a pressure differential between the plenum and the compartment, as a result of which the heated air is forced through the partition into the spaces between the packages to heat the food therein, the heated air also flowing in a continuous loop about the compartment through the passages to thermally isolate the compartment. In the heat-up phase, the heated air takes the form of a pulsatory wave in which the pulses are at a temperature above the service level separated by lower temperature intervals during which heat from the outer layer of the food is transferred into the body thereof to prevent the food from being heated above the service level. In the subsequent service phase, the temperature of the air is held at the service temperature level.