A heating assembly, comprising a primary heating tube made of electrically conductive material and forming at least part of an inner tube; an auxiliary heating tube made of electrically conductive material and forming at least part of an outer tube; a pair of flanges which mechanically and electrically interconnect the inner tube with the outer tube, wherein the inner and outer tubes (110,120) extend between the flanges with the inner tube arranged inside the outer tube, wherein the primary and auxiliary heating tubes (110H, 120H) axially overlap at least along a subsection length of the inner and outer tubes (110,120), respectively, between the flanges; wherein, along the subsection length, an inner wall surface of the auxiliary heating tube faces an outer wall surface of the primary heating tube for transferring auxiliary heat from the auxiliary heating tube to the primary heating tube over a radial gap between the inner and outer wall surfaces (121, 111); and a pair of electrodes (130, 131), connected to respective parts of the electrically conductive material and arranged for forming an electrical path through the primary and auxiliary heating tubes (110H, 120H) via the electrically conductive material; wherein the outer tube comprises an electrically insulating section arranged for mechanically connecting, while electrically separating, parts of the electrically conductive material, to have the electrical path exclusively passing in series through respective parts of the primary and auxiliary heating tubes (110H, 120H); characterized in that the auxiliary heating tube comprises an extendible section, configured to axially extend or shorten for compensating any difference in thermally induced contraction or expansion, respectively, between the inner tube and the outer tube. a primary heating tube made of electrically conductive material and forming at least part of an inner tube; an auxiliary heating tube made of electrically conductive material and forming at least part of an outer tube; a pair of flanges which mechanically and electrically interconnect the inner tube with the outer tube, wherein the inner and outer tubes (110,120) extend between the flanges with the inner tube arranged inside the outer tube, wherein the primary and auxiliary heating tubes (110H, 120H) axially overlap at least along a subsection length of the inner and outer tubes (110,120), respectively, between the flanges; wherein, along the subsection length, an inner wall surface of the auxiliary heating tube faces an outer wall surface of the primary heating tube for transferring auxiliary heat from the auxiliary heating tube to the primary heating tube over a radial gap between the inner and outer wall surfaces (121, 111); and a pair of electrodes (130, 131), connected to respective parts of the electrically conductive material and arranged for forming an electrical path through the primary and auxiliary heating tubes (110H, 120H) via the electrically conductive material; wherein the outer tube comprises an electrically insulating section arranged for mechanically connecting, while electrically separating, parts of the electrically conductive material, to have the electrical path exclusively passing in series through respective parts of the primary and auxiliary heating tubes (110H, 120H); characterized in that the auxiliary heating tube comprises an extendible section, configured to axially extend or shorten for compensating any difference in thermally induced contraction or expansion, respectively, between the inner tube and the outer tube.