Abstract: A heating device for a fluid storage tank is provided. The heating device comprises a heat tube including first and second elongate hollow legs which are joined together at an angle relative to each other so as to enable fluid flow therebetween. The first and second hollow legs being at least partially filled with a heat transfer fluid and being adapted to be disposed in a fluid storage tank with one leg extending generally longitudinally relative to the tank and one leg extending generally transversely relative to the tank adjacent a bottom wall of the tank. A heater is arranged in an aperture adjacent one end of the first elongate hollow structure. A safety relief valve can also be arranged on the heat tube so as to enable venting of an excess pressure condition of the heat transfer fluid.