In this paper, we propose a clustering algorithm to enhance the performance of fixed wireless sensor and actuators networks (WSANs). In each cluster, a multi-level hierarchical structure can be applied to reduce the energy consumption. In addition to the cluster head, some nodes can be selected as intermediate nodes, each of which manages a subcluster, according to their positions. Intermediate nodes aggregate data from general nodes and send them to the cluster head. The selection of intermediate nodes to optimize energy consumption can be considered as mixed-integer linear programming having high computational complexity; consequently, a lowest energy path searching algorithm is proposed to shorten the computational time. Simulation results indicate the potential to prolong network lifetime in WSANs.