The report describes an investigation of the adequacy of a modeling approach in predicting the thermal environment and flow field of pulverized-coal-fired utility boilers. Two 420 MWe coal-fired boilers were evaluated: a single-wall-fired unit and a tangentially fired unit, representing the two commonest boilers in the U.S. Extensive field measurements were conducted on each unit to determine detailed temperature, heat flux gas species composition, and flow field data for a range of operating conditions. Separate modeling approaches were used to predict boiler thermal performance and flow characteristics. A three-dimensional zone method of analysis was used to predict local and overall heat transfer, temperature profiles, and fuel burnout. Such predictive tools provide a sophisticated treatment of radiative heat transfer, but are decoupled from the furnace flow field. This input to the heat transfer code was obtained from detailed measurements in reduced scale isothermal physical flow models of the two boilers. Comparisons between model predictions and the detailed field measurement data have demonstrated the viability of this approach in predicting furnace performance, and in extrapolating limited available data to alternate operating conditions. Overall thermal performance can, in general, be predicted accurately.