Solar radiation is a renewable non polluting energy source which can be used in buildings through various systems technologies. Thermal radiation, absorbed or transmitted by the walls and windows, creates a solar gain which has a direct impact on the thermal behavior in the building. Most existing thermal models neglect the effect of the evolution of the sun patch position on the heating floor which can have a great impact on the indoor thermal comfort. In this paper, we present numerical model to calculate the transient sun patch position and its influence on the heating floor model in order to evaluate its impact on the heating floor operating conditions and on the indoor air temperature, which has a great influence on thermal comfort under the climatic conditions of Oran city in Algeria. The sun patch is calculated using Ray Tracing model as proposed in FLUENT whereas the room and the heating floor are modelled with TRNSYS software. Using literature data, the two proposed models (sun patch model and heating floor model) are validated and used to simulate the cases with different geographic locations and different window orientations, surfaces, and positions. Our results suggest that the displacement of the sun patch on the heating floor lead to a superheating of the irradiated zone and it affects the indoor air temperature and thermal comfort too. (C) 2016 Elsevier B.V. All rights reserved.