Apparatus and method for rapidly heating one or more reactants for use in a fuel reformer. The apparatus includes a combustion section having an outer wall enclosing a combustion chamber and a catalyst disposed within the combustion chamber. A heat recovery section is in fluid communication with the combustion section and has an outer wall defining a heat recovery chamber. At least one heat exchanging element is located within the heat recovery chamber having an inlet for receiving a fuel reforming reactant and an outlet for directing a heated reactant out of the heat recovery section. The combustion section is elevated relative to the heat recovery section such that heated combustion gases are displaced down into the heat recovery section. The housing has an internal diameter of less than about 10 inches, or alternatively, has a length and a diameter in a ratio of between about 7:1 and about 4:1.