Abstract: An apparatus for heating liquid media, especially for the heating of used oil during its reprocessing by cracking distillation, includes at least one infrared irradiation element located in a vertical cracking vessel. The irradiation elements are separated from the oil to be heated by spaced infrared permeable tubes of quartz glass having cooled intermediate spaces therebetween. The spaced tubes allow the infrared energy to pass unobstracted into the vessel and the intermediate spaces therebetween prevent heat transfer by convection or conduction to the oil. The cracking of the used oil is thus carried out without the formation of undesirable deposits of bituminous substances within the vessel, and especially upon the irradiation elements.