The invention relates to a method for extracting heat from an effluent (2) circulating in a conduit (1), especially a waste water collector, according to which a heat exchanger (E) is installed, at least in the bottom of the conduit, said heat exchanger (E) lying in the effluent and being formed by coating tubes (3) with sufficiently heat-conductive concrete cast around the tubes intended for the circulation of a heat-transfer fluid, the heat exchange with the effluent of the conduit being carried out through the moulded coating. The concrete (4) of the coating consists of at least 50 weight % of silicon carbide, a load of needles made of a heat-conductive and mechanically resistant material, a binding agent and the remainder of alumina, metal powder or carbon.