We investigate the effectiveness of cluster-based routing protocols in extending the lifetime for energy-constrained wireless sensor networks. Most routing protocol designs for wireless sensors exploit the fact that they are not communication networks in the classical meaning. They can rather be considered as distributed systems where all the different entities collaborate to perform a given task or set of tasks. This fact is used to trade per node fairness and other networking qualities for designs that are energy efficient. The networking layer is responsible for the end to end routing and delivery of data messages. Routing decisions affect the number of transmissions, the distance covered per transmission and the load placed on the intermediate nodes that participate in relaying the messages. This makes the design of energy efficient protocols in the routing layer very critical for extending the network lifetime. For these reasons, the network layer has attracted more attention than the other layers for energy-efficient designs. This study focuses on common parameters of well-known cluster based routing protocols.We use LEACH protocol as a representative to investigate their energy performance sensitivity to the number of clusters, the location of the base station and the data message size.