Rapid motorization in developed and developing countries demands more parking spaces in urban areas. Underground car parking space in multi story buildings offers viable solution. However, lack of natural ventilation accumulates the harmful emissions from cars, operating in underground car parks. Exposure to these hazardous pollutants causes health risk to the users. Therefore, proper mechanical ventilation system should be adopted for the removal of harmful pollutants. This paper discusses the usage of modeling and simulation tools in the design of the mechanical ventilation system. Two widely used modeling techniques, multi-zone modeling and CFD modeling were used to simulate the contaminant distribution in a mechanical ventilated environment. The former provides an approximate macroscopic solution of the carbon monoxide (CO) distribution, while the later provides precise distribution of CO contours. The two models were validated against field measurements made at Chennai, India. The model predictions were very close to the actual site measurements. The impact of garage height and CO generation rate on ventilation requirement has been analysed.