This study analyses the effects of the radiation exchange inside a horticultural greenhouse, under winter climatic conditions, according to the number of squared heating tubes used. These ones, hot and isothermal, are equidistant inside the greenhouse volume. The governing differential equations are discretized using a finite volume method and the coupling pressure-velocity problem is carried out by the SIMPLER algorithm. The algebraic systems obtained are solved by a conjugate gradient method. Results are reported in terms of isotherms. streamlines and average Nusselt number for Rayleigh number of 10(3)- 10(6). The contour lines show that the radiative effects are noted near the solid surfaces, and become increasingly important when the Rayleigh number increases. As a result, the rise in the value of Rayleigh number leads to an increase of the overall heat transfer within the greenhouse. (C) 2009 Elsevier Ltd. All rights reserved.