Abstract: A device including a side wall (3) and bottom walls (4, 5) together forming a metal vessel (2) containing a core (7) for exchanging heat between two fluids, i.e. preferably counter-flowing heating and heated fluids. The core is arranged vertically within the chamber and radiates heat towards the inner surface of the side wall through an intermediate space (24) provided between said wall and the core and filled with a fluid which is the same as or different from one of the fluids flowing therethrough. The chamber is cooled both by exposing the side wall (3) to the atmosphere and by using a thermosiphon effect to cause the fluid in the intermediate space (24) to flow through a closed circuit (30) including said intermediate space and at least one pipe (31) located outside the chamber and connected thereto at two vertically spaced points. The device may be used in oil industry exchangers.