Accurate prediction of ventilation flow is of primary importance for designing a healthy, comfortable and energy-efficient indoor environment. Since the 1970s, the use of computational fluid dynamics (CFD) has increased tremendously and nowadays it is one of the primary methods to assess ventilation flow in buildings. The most commonly used numerical approach consists of solving the steady Reynolds-averaged Navier-Stokes (RANS) equations with a turbulence model to provide closure. This paper presents a detailed validation study of steady RANS for isothermal forced mixing ventilation of a cubical enclosure driven by a transitional wall jet. The validation is performed using particle image velocimetry (PIV) measurements for slot Reynolds numbers of 1,000 and 2,500. Results obtained with the renormalization group (RNG) k-e model, a low-Reynolds k-e model, the shear stress transport (SST) k-¿ model and a Reynolds stress model (RSM) are compared with detailed experimental data. In general, the RNG k-e model shows the weakest performance, whereas the low-Re k-e model shows the best agreement with the measurements. In addition, the influence of the turbulence model on the predicted air exchange efficiency in the cubical enclosure is analyzed, indicating differences up to 44% for this particular case.