Although Computational Fluid Dynamics has become a very popular topic in recent years, the main areas of study have focused on machine tools and climate control. Major reasons for this is the resources available. If a finer mesh is used, the computational domain has to be relatively small. Through the use of the Kyoto University’s Super Computer, successful simulation was established of fluid flow in a multi story building. This paper will discuss the model that is used to simulate the fluid flow in a full scale three story building. In particular the heat flow in the building. This multiphase model will not only discuss the velocity and thermal profiles in a 3D environment, but also the interaction between the heated air flow and the different materials. The interaction between fluid and the different solids will be discussed. The paper will first compare the numerical results with existing experimental results done on similar multistory structures.  Further more, the paper will compare different heating locations and methods. This is in order to find the optimum conditions required to heat the building quickly. The successful simulation will be shown that gives the best results for the heating in the multistory building. The model is compiled in a Fortran compiler, parallelized using MPI. The structure was constructed using FEMAP software. The paper will also discuss the computational time required for the given mesh size.