An air curtain should be mounted inside the door.
If you mount an air curtain outside of a door, it will not keep out the heat transfer that occurs between the outside and the inside of a building. This means that you will continue to pay for heating or cooling even if your doors are closed. Mounting an air curtain inside of your doors will help you save money and energy by keeping out heat transfer that occurs from the outside, keeping your home or business at optimal temperatures.