In the development of future fighter aircraft it is important to reduce unnecessarytime consumption. The geometry in the aircraft is essential to examine in an earlystage so it fulfills necessary demands, such as ventilation. To simulate ventilationflow is costly with large 3D simulations. Therefore, new ways of investigating fluidflow are looked upon. The objective of the study is to develop a 1D simulationmodel for aircraft ventilation systems. The purpose is to reduce the lead times inconstruction of aircraft as the 1D model can be used early in the design process, this1D model can also be used for parametric design and optimization. 3D simulations,using CFD, have high computational costs and need precise design parameters,resulting in longer lead times. The programs used throughout the study are STARCCM+for the CFD simulation and OpenModelica for the 1D simulation. TheCDF model is used to predict the mass flow through the ventilation system. A 1Dsimulation is implemented to simulate the same system with satisfactory accuracyusing 1D equations and simplifications. The CFD model and the 1D model arecompared in three different steady-state cases. The accuracy of the model rangesfrom 1%-9%, in the different flight cases. The relative error is higher for cases withhigher speeds, with a theory that the boxes in the domain, which are not accountedfor, give a significant error for higher speeds. However, the 1D tool offers a fast andpractical tool in an early design process, while the 3D CFD remains essential fordetailed and complex 3D flows.