A preheat fuel delivery system includes a fuel processor and a source of vaporized fuel. Vaporized fuel is feed into the inlet fuel port of the fuel processor. An outlet fuel port of the fuel processor is connected to an intake port of a combustion source. An exhaust port of the combustion source is attached to an exhaust intake port of the fuel processor. The heat from the exhaust gases of the combustion source heat the vaporized fuel inside the fuel processor. A first embodiment of the fuel processor contains a plurality of plates. A second embodiment of the fuel processor utilizes a plurality concentric tubes. A third embodiment of the fuel processor includes two concentric tubes.