In recent years clearing the mist on side windows is one of the main criterions for all OEMs for providing comfort level to the person while driving. Visibility through the side windows will be poor when the mist is not cleared to the desired level. “Windows fog up excessively/don't clear quickly” is one of the JD Power question to assess the customer satisfaction related to HVAC performance. In a Mobile Air Conditioning System, HVAC demister duct and outlet plays an important role for removing the mist formation on vehicle side window. Normally demister duct and outlet design is evaluated by the target airflow and velocity achieved at driver and passenger side window. The methodology for optimizing the demister outlet located at side door trim has been discussed. Detailed studies are carried out for creating a parametric modeling and optimization of demister outlet design for meeting the target velocity. In this methodology, a parametric modeling of demister outlet design using the factors such as length, width, vane angles and demister outlet to window angle is created using CATIA. Design for six sigma methodologies is followed for robust optimization and arrive at the combination of appropriate design factors which influences the velocity at side windows. L18 orthogonal design array matrix has been created and flow simulations are carried out using the commercial CFD software STAR CCM+. The impacts of each design factors and levels on the side window velocity have been analyzed extensively and best combination of design factors have been found out. Parametric modelling of demister outlet significantly aids in reducing the manual design time for simulation by 50% and DFSS approach helps in finding out the optimized design factors of demist outlet during the design phase of new programs.