An apparatus for heating an insulation fluid in a medium-voltage or high-voltage switchgear comprises an infrared source which is adapted to emit infrared radiation of at least one wavelength. Thus, at least one vibrational or rotational mode of at least one component of the insulation fluid is excited by absorption of at least a part of the infrared radiation, and condensation of the insulation fluid is efficiently prevented by this direct heating of the insulation fluid. A closed loop temperature regulator is used to heat only when required. A circulator in a heating chamber further provides for a mixing of the insulation fluid, thus preventing steep temperature gradients.