The invention concerns a device for extracting heat from gas, in particular combustion gas, containing dust and/or condensable substances to recover condensates, and comprising at least one heat exchanger (4) including a chamber (13) having a symmetry of revolution surrounded by a cooling envelope. The invention is characterized in that it comprises an orifice (9) for allowing through an agent for treatment surface of the inner surface of said chamber, said chamber (13) being moreover provided with at least a screw with helical pitch arranged coaxially in a tube (14).