This paper presents a validated model based on the object-oriented modeling tool based on Modelica approach for the radiant floor heating system, located in thermal laboratory in a test building. The system consists of heat pump, radiant slab, circulation pump, three way valve and hydraulic loop. Single circuit radiant slab was the main component in our Modelica model. A comparison of simulated and measured data for two case studies resulted in maximum absolute error for room temperature, surface temperature, convective heat flow and radiative heat flow as 0.914°C, 0.772°C, 2.5W/m² and4.5W/m² for the first case study and 1.192°C, 1.463°C, 2.275W/m² and 3.9W/m² respectively for the second case study. The simulated results agreed very well with the measured data by taking the measurements errors and the simulation assumptions into account. Therefore, the developed model was validated to be applicable in other projects.