Abstract: In order to prevent a conduit for heat absorption from a sea bottom or the like to float up in wintertime from the bottom due to icing, it is proposed according to the invention that the flow cross-section of the conduit is heat insulated from the surrounding water. Such insulation is obtained according to one embodiment of the invention, in that a work fluid is imparted with a laminar flow in the upper cross-section (15) of the conduit by means of a constricting inner pipe (12) located upwardly in the conduit, while the work fluid in the remaining cross-section (16) is permitted to have a turbulent flow.