An electric heater to heat a flow of a fluid having a jacket block comprising a plurality of longitudinal bores to allow the through-flow of a gas phase medium. An elongate heating element extends through each of the bores and is positionally stabilised relative to the jacket block via at least one support member, optionally in the form or an elongate rod to inhibit undesirable independent axial and/or lateral movement of the heating element relative to the jacket block.