Thermal large eddy simulations are carried out in order to study the convective flow in a solar receiver. We investigate the impact of thermal gradients on a turbulent channel flow with imposed wall temperatures for two turbulent Reynolds numbers based on the friction velocity (180 and 395). In this configuration, the flow is subsonic, while temperature variations can be strong and induce significant variations of the fluid properties. The low Mach number equations are considered. The influence of the variations of the conductivity and the viscosity is first investigated. We show that the influence of these properties can be considered constant only for weak temperature gradients. The thermal subgrid-scale modeling is studied and we conclude that for a temperature ratio of 2, we can use a constant subgrid-scale Prandtl number. Finally, we focus on the increase of the temperature ratio that emphasizes the flow dissymmetry and modifies the fluctuations profiles. The physical mechanism responsible for these modifications is explained.