This paper addresses the modeling of convective and radiative heat transfer to achieve an acceptable level of indoor temperature. The results presented were obtained in a pilot project in which an energy-efficient house was built on a site located west of Algiers. The main objective was to perform a numerical simulation to investigate how the temperature of the heat-transfer fluid circulating in the floor heating system affected the temperature of the indoor air and also how surface radiosity affected the temperature profile of the indoor air. The study employed the finite element method integrated into the Comsol Multiphysics software. The model was validated using experimental data reported in the literature for the pilothouse at the same meteorological conditions. An error of about 2.32% was apparent between the experimental and theoretical results. Results showed that the increase of the heating transfer fluid temperature from 30 to 50 °C produced the same temperature of about 15.1 °C taken at a 50 cm height inside the room. The air temperature remained stable, with an insignificant variation after 72 h of heating. Surface radiosity increased as a function of time and reached an almost constant value of 380 W·m−2 after 72 h because of the stability of the air temperature by convection.