The heating process in multizone resistance furnaces, as applied to floating-zone crystal growth, is analyzed. A global model is formulated, where the temperature fields in the sample, the furnace and the insulation are coupled; the input thermal data is the electric power supplied to the heaters; the thermal conductivity of the insulation is modeled with the aid of experimental results. The radiation heat exchange between the sample and the furnace is formulated analytically, taking into account specular reflections on the sample; in general, for solid samples the reflectance is both diffuse and specular, and for some melts it is mostly specular. This behavior is modeled through the exchange view factors, which depend on whether the sample is solid or liquid, and, therefore, they are not known a priori. The effect of this specular behavior on the temperature field is analyzed, and compared with the case of diffuse samples; this effect is shown to be important in the analysis of the melt zone, for instance, differences of the order of 100% are obtained in parameters like the melt length or the maximum temperature difference in the melt when specular reflections are neglected. The model is used to simulate the heating process in the floating-zone technique in microgravity conditions; parameters like the Marangoni number or the temperature gradient at the melt-crystal interface are estimated. The model is validated comparing with experimental data. (C) 2002 Elsevier Science B.V. All rights reserved.