A thermoelectric system should be designed in such a way that it harvests as large water heat as possible while using the least modules. To seek an optimal module number, the present study investigates the effect of source temperature, mass flow rate, turbulator, module number and layout on performance of a thermoelectric generator (TEG) system. The experimental results show the optimal module number isn't a fixed value and turbulator has a significant influence on the whole performance of the thermoelectric system. For compact configuration of TEG, using six modules is the best choice without a turbulator, while using eight modules has the best performance with turbulator. The study shows that module layout has a great effect on the thermoelectric system performance. Compared to compact configurations, all separate ones can harvest more power from the hot air except for 32 modules, enhancing by 10–50% whether the turbulator exists or not. In this situation, eight modules are optimal number. The net output power achieves a maximum value of 16.93W and the maximum net efficiency is 3.85% under present experimental parameters. Meanwhile, a new index called power uniformity coefficient is introduced to assess the distribution of output power among TEGs.