The size of the hood is important. For a 12' hood, you'll need approximately 4000 CFM. The size of the hood and exhaust fan should match the overall space. For a larger sized commode, consider a higher-performance hood. A commercial aeration system will allow you to cook more food without compromising the airflow. To avoid this problem, you may want to consider installing a Make-up Air (MUA) fan. The MUA fan can also be installed as an option.
Once you've chosen your hood, consider the hood's performance. The volume of air being exhausted will depend on the type of cooking being done. If you're using open-flame cooking, the resulting thermal plume will produce more grease. The duct design of a commercial kitchen exhaust system should be appropriate for the appliance's size and performance. A professional commercial exhaust cleaning company will be able to help you with the design.