A heat pack includes a housing, a first phase change material (PCM) that is contained in the housing, and a thermal storage buffer that is contained in the housing. The thermal storage buffer includes a second PCM. An initiator is in operative contact with the first PCM. Activation of the initiator causes crystallization of the first PCM, and the first PCM cooperates with the thermal storage buffer to provide heat at a predetermined temperature range upon crystallization of the first PCM.