From a FS perspective, the main or front door in a house or a shop-front and the entrance to a retail shop is called the the “Na Qi Kou” 納氣口 or “Received Qi Mouth”, sometimes it is referred to simply as the “Qi Kuo” or the “Qi Mouth”. In the “Foundation of Yang Dwelling” part of the book “Gui-Hou Lu” 《歸厚录》(Record of Returning to the Profound), it is said, “A Yang dwelling is built on earth, but it is not only the Earth Qi that we need to consider but also how to take in the Door Qi. Let it be empty and open so horizontal movement is free, once the door is open, the Qi will enter from the door”. “阳宅作在地上，不专以地气为用，兼取门气。盖清虚之让，气本横行，门户一开，气即从门而入”. The “Qi Mouth” is like breathing that keeps us alive, the whole house relies on the Qi comes in and goes in in an unhindered way. The FS of the Na Qi Mouth keeps the a household happy and healthy, and the Na Qi Mouth of a business keeps its wealth flowing and the vitality lasting. We need to pay special attention to all the Na Qi Mouth(s) of a building, every time we do Feng Shui.
Look at this lovely traditional shopfront window of a Miso Soup Shop in the Hiroshima Prefecture of Japan (pictures taken from the Window Research Institute of the Tokyo University of Technology). Sadly, we do not build like this any more.