The size of the window should be normal. If a window is too big, it causes too much Qi currency. In summer, too much heat comes into the house/apartment; In winter, too much heat flows out from the house/apartment. If a window is too small, it is not easy to get fresh air. On another side, the people living in the room become stingy and introversive.
The number of window should be normal, otherwise it is not easy to get Qi balance in the room, so that the family life becomes stressful.
The top of the windows must be higher than the persons living in the room, otherwise it hurts the confidence of them.
The recommanded forms for windows are arc, round or square. Arc and round windows create peaceful and calm atmosphere, while square windows give stable and upgoing feeling to the people. Man can choose different forms according to the functions of the rooms. For example, round or arc windows for bedrooms and corridors, and square windows for offices.
East: The windows in east get much Yang Qi from the nature. They are good for complementing the positive Feng Shui to the house/apartment.
North: The windows in north get much Yin Qi from the nature. They increase the negative Feng Shui to the house/apartment.
South: It is usual to locate windows in the direction. This direction is good for receiving Yang Qi from the nature.
Southeast: Windows in this direction are good for adjusting the indoor temperatures. In sommer, they are good for decreasing the temperatures. In winter, they are good for keeping the indoor heat.
West and northwest: Windows in these directions are not good for keeping indoor heat. If you don't use the rooms in winter, it doesn't matter to locate the windows in the directions.
Northeast and southwest: It is not usual to locate windows in these directions.