The present study is devoted to the analysis and prediction of the efficiency of air curtains. The attention is focused on improving existing semi-analytical methods with the information from CFD simulations and experimental measurements. The goal is to obtain an accurate simplified model which describes the three-dimensional behaviour of the air jet without requiring large time consuming calculations. The interaction of the air curtain with other agents, e.g. pedestrians and flying insects, is also revised. The model is validated against both experimental data and advanced LES calculations carried out by the authors. Furthermore, a parametric study shows the air curtain behaviour for different configurations.