Controlling the cleanliness and limiting the fouling and slagging of heat-transfer surfaces are absolutely necessary to optimize boiler performance. The traditional way to clean heat-transfer surfaces is by sootblowing using air, steam, or water at regular intervals. But with the advent of fuel-switching strategies-such as switching to PRB coal to reduce a plant's emissions-the control of heating surface cleanliness has become-more problematic for many owners of steam generators. Boiler modeling can help solve that problem.