The use of open-source CFD has been growing in both industry and academia. Open-source CFD saves users a considerable license cost and provides users with full transparency of implementation and maximum freedom of customization. However, it is often necessary to assess the performance of an open-source code before applying it to the practical use. This study applies one of the most popular open-source CFD codes – OpenFOAM to theindoor airflow and heat transfer prediction. The performance of OpenFOAM is evaluated and validated against awell-documented benchmark test. Various OpenFOAM built-in turbulent viscosity models are attempted withinthe framework of Reynolds Averaged Navier-Stokes Simulation (RANS) approach and the simulation results arecompared to the experimental data. Among all models, the 𝑘 − 𝜔 𝑆𝑆𝑇 model has shown the best overall performance, whereas the standard 𝑘 − 𝜀 model is the most robust one despite its deficiencies. The results of this study demonstrate the capability of OpenFOAM in the field of indoor air simulation and promote users confidence in using OpenFOAM in their research work.