Combustion modifications (e.g., low excess air firing, staged combustion) can decrease NOx emissions from coal-fired utility boilers. However, these operating conditions may affect the rate of tube wall corrosion by creating chemically reducing environments in the furnace. Therefore, this study was designed to measure boiler corrosion rates as well as the effects of certain combustion modifications (CM) for NOx control. This report deals with Boiler No. 2 at Utah Power and Light Co.'s Hunter Generating Station in Castle Dale, Utah. Initially, the boiler was characterized to determine the short term effects of CM on boiler emissions and performance. Later, NOx and other emissions were monitored continuously during several 30-day periods so that longer term operations could be evaluated. Finally, a study of corrosion rates inside the furnace helped to determine the corrosion effects of low-NOx operation. At Hunter No. 2, a special Low-NOx Concentric Firing System (LNCFS) was installed by Combustion Engineering, Inc. The LNCFS deflects some of the combustion air away from the fuel jets and toward the furnace walls to decrease both NOx emissions and corrosion effects. In these tests, the LNCFS together with other combustion controls were able to decrease full-load NOx emissions during both normal long term operation and shorter well-controlled tests using extreme CM.