Network coding is expected to improve throughput performance of multihop wireless networks. However, the throughput performance is significantly affected by the coding overhead at intermediate nodes. In this paper, we consider the trade-off between the throughput and coding overhead. Focusing on an intermediate node of a three-node chain topology, we model it as a single-server queueing system with two buffers. The per-flow throughput is analyzed with a continuous-time Markov chain, and the analysis is validated by simulation. Numerical results show that the analytical results agree fairly well with simulation when the offered loads of the flows are the same. It is also shown that a long processing time for coding causes a significant reduction in throughput.