How big is the bedroom window for Feng Shui?

The windows should be as large as possible and have the best insulation and feng shui. It is large and has advantages in ventilation, breathability and lighting. However, the large windows were not conducive to heat preservation in the past, and there were difficulties in winter, so I had to think that it was better to go smaller. On this issue, modern society has completely broken through the historical prohibitions. The main reason is that glass has made a great contribution. With glass, opening the windows can provide ventilation and good air circulation, and closing the windows has excellent heat preservation effect. This is the superiority brought to mankind by human progress and scientific development. Historically, there was no glass and other building materials were not comprehensive, so the cold winter was unbearable without windows, but in the summer, the windows were small and the heat was unbearable.