In the present work, comprehensive CFD and experiment investigations are performed on the integrated hot box components to determine the optimal operating conditions for 1 kW-class SOFC stack system fueled with natural gas. In the first part, CFD models are implemented on the standalone reformer to make different reformate compositions to determine which composition can provide best stack performance keeping in mind fuel/air utilizations, thermal gradients effect on the stack cells due to internal steam reforming and the parasitic excess air for stack cooling. The parameters that are studied in the simulation includes steam to carbon ratio, the temperature of the reforming tube, effectiveness factors, and methane conversion. The validation and calibration of the numerical model are accomplished through comparison with experiment (also performed on standalone reformer placed in the furnace) reformate compositions and conversion. In the second step, simulations using validated model have also performed on the real-scale integrated hot box components (steam generating tube, reformer, and combustor) to ascertain the performance and effectiveness of this design. Anode and cathode off-gases are burnt in the combustor to provide the necessary energy to execute the methane steam reforming process. The waste heat recovery and compactness due the reformer combustor integration increase the system efficiency. Numerical calculations on different heat exchanger (HX) designs installed around the cells are also performed separately by fixing the boundary conditions obtained from experiments. From the numerical calculations on the full-scale system, it is found that for the SOFC operating temperature of 750°C, combine mole fraction of H₂ and CO is ~0.79 for effectiveness factor of 0.02, s/c of 2.5 and methane conversion of 76% which is comparable to the electrically-heated reformer.