A 5 kW class shell and tube methane steam reformer with intermediate temperature heat source was evaluated for the efficiency boost up of high temperature fuel cell system. The shell side of shell and tube steam reformer is consisted of inlet compartment, outlet compartment and reforming zone. Tube sides are filled with 37 tubes to maximize the heat transfer area between the reforming zone and heat source zone. Among the various operational conditions of the reformer, reformer reactants flow rate, steam to carbon ratio, reformer inlet temperature, and heat source inlet temperature are changed to find the crucial factor on low temperature reforming reaction. Additionally, transient behavior of the reformer is considered during the start-up of methane steam reforming reaction at low temperature. The results show that the main factors for affecting the performance of the reformer are load and heat source inlet temperature. (C) 2019 Elsevier Ltd. All rights reserved.