The objective of the study was to create a simple CFD (Computational Fluid Dynamics) model of colliding isothermal jets from two identical ceiling diffusers facing each other and to study the influence of the distance between the diffusers on the resulting downward jet. The modelling was done using a commercial CFD (Computational Fluid Dynamics) code. Air flows were visualised with smoke in order to analyse the collision point and flow behaviour after the collision. Velocity measurements were carried out to obtain velocity profiles for the supply air diffusers to be used as initial conditions in the CFD simulations. In addition, measurements were made to determine velocity magnitudes in the collided jets at the occupied zone. Different turbulence models were used in the simulations and compared to the visualised and measured data. As a result a valid CFD model describing the behaviour of the two colliding isothermal jets was created. It was concluded that the CFD models adequately described the phenomena and provided useful data to be used in further studies.