In devices known in the art, "conventional firetube" and "waste heat recovery" boilers each require many small tubes making successive passes within the boiler. In one embodiment of the invention, however, an enhanced conduit replaces numerous conventional small tubes. In some embodiments, the enhanced conduit incorporates a plurality of fins, each of which extends through a wall of the conduit. In other embodiments, the enhanced conduit incorporates a plurality of tubes along its outer surface, through which a heat transfer medium flows. Both designs enhance the heat transfer relationship between the hot fluid and the heat transfer medium by providing a continuous heat transfer relationship with the heat transfer medium, increasing the surface area involved in the heat transfer relationship and enhancing convection/conduction couples. For some applications, all of the tube banks of other devices in the art can be replaced by one continuous enhanced conduit.