I've noticed that stores blow hot air in a "sheet" by doors and windows, which is "where cold air enters". I assume they do this because it saves money and/or keeps the store a uniform temperature. But why? If this works, how does it work?
I am looking for a mathematical or fluid-dynamics answer, if possible.
In fact it's quite the opposite : cold places in a room are due to contact with the cold outside : door, window, bad isolation ... So putting heater here make you also heat the outside, and waste some money.
The reason to do so is that the point of a heater is to make cold places hot : as you said you want an uniform temperature.
