Biomass boilers play a pivotal role in reducing carbon emissions by using organic materials such as wood and agricultural residues as fuel, rather than fossil fuels. The challenge in the design and analysis of these boilers lies in developing computationally efficient and accurate models to simulate these complex systems. While Computational Fluid Dynamics (CFD) provide detailed and reliable results, they are computationally expensive and time-consuming. In contrast, zero-dimensional (0-D) models offer a simplified representation that sacrifice spatial detail for computational efficiency. These models therefore offer a simplified yet efficient way to simulate key combustion and heat transfer processes with significantly reduced computational demands. This paper evaluates existing empirical 0-D models by comparing their results to benchmark solutions obtained with detailed CFD simulations for two bagasse-fired boiler case studies, namely a 105 t/h industrial-scale boiler and a compact 45 t/h boiler. The comparison reveals that although the total energy flows are generally consistent between the 0-D and CFD models, there are differences in the heat transfer distribution and temperature predictions. These findings highlight the need for further calibration of 0-D models to improve their accuracy, especially for smaller biomass boilers.