Energy and exergy analyses were previously performed by the authors of a coal-fired steam power plant. These analyses suggest that the steam generator (and its combustion and heat-transfer processes) is the most inefficient plant device and that significant increases in overall plant efficiency are possible by reducing steam-generator irreversibilities. Here, a possible plant alteration is examined to increase the efficiency of the plant by reducing the irreversibility rate in the steam generator. The modification involves decreasing the fraction of excess combustion air from 0.40 to 0.15. The results show that overall-plant energy and exergy efficiencies both increase by 1.4% when the fraction of excess combustion air decreases front 0.4 to 0.15. Copyright (c) 2006 John Wiley & Sons, Ltd.