A model for the energy consumption of anode as a function of its throughput in a wireless CSMA network is proposed. First model a single-hop network, and then a multi-hop network. The CSMA network operated at a high throughput is energy inefficient since unsuccessful carrier sensing attempts increase the energy consumption per transmitted bit. Operating the network at a low throughput also causes energy inefficiency because of increased sleeping duration. Achieving a balance between these two opposite operating regimes, the authors derive the energy-optimum carrier-sensing rate and the energy-optimum throughput which maximize the number of transmitted bits for a given energy budget.