A numerical procedure for heat transfer in a circulating fluidised bed boilers (CFBB) is presented. The riser of these units has, typically, a low height to width ratio, of order of ten, and low net solids flux. Refractory walls involve the bottom bed and two membrane walls are use to confine a square cross-section conduct that works as the riser of the CFBB. The considered unit uses group B particles according to the Geldart classification, with mean diameters of 500 µm and density of 2500 kg/m 3. The present work is part of a combined effort to develop a complete numerical package to be used in the design of CFB boilers. It only concerns the different features of the heat transfer in CFBB, namely heat transfer coefficients, temperature profiles, its dependencies on fluid dynamic and combustion models, and the calculation of the total thermal power output. The fluid dynamic and combustion models were developed by other teams. Fluidised bed heat transfer occurs essentially by two mechanisms: convection and radiation and despite showing a complex coupling, they are usually assumed as additive. A CFBB is a complex system, constituted by three main parts: the riser, where the combustion occurs and the particles are fluidised and transported; the cyclone, with the purpose of separating the particles from the gas flow and the downcomer, providing the recirculation of the material back to the riser. The present work concerns only the riser, where the majority of the heat transfer occurs. Considering the dynamic structure of the riser, the heat transfer is present in three different fronts: from nucleus towards annulus, from nucleus towards the wall through the annulus, and directly from annulus to the wall. Except for beds with low particle concentration values, convection is the dominant mechanism (Breitholz and Leckner, 1997). The numerical procedure is applied in layers of infinitesimal height, in order to be possible to solve the energy, the momentum and the continuity equations, and an irregular mesh was used. The bubbling portion of the bed and the splash zone are composed, each one, by a single layer; this approach is a function of the hydrodynamic model upon which the heat transfer model is based. For the core-annulus zone, two columns of infinitesimal layers were used. In fact several meshes are used, concerning fluid-dynamic properties, heat transfer properties and geometrical features.