An auxiliary heater for motor vehicles includes an open housing accommodating a layered structure which includes at least one radiator element and at least one heat-emitting element having at least one PTC heating element, and further accommodating at least one spring element pretensioning the layered structure, a plurality of contacts being held in said housing in an insulating manner and electrically connected to the at least one PTC heating element. The layered structure is pretensioned by a displacer which is inserted into a lower housing component when the elements of the layered structure have been inserted in the lower housing component in a tension-free manner. The displacer is inserted into the lower housing component in a direction approximately perpendicular to the plane of the layered structure and, in the mounted position, it is secured in position relative to said lower housing component.