Earlier, farmers had no conditions to wash their feet every day, let alone soak their feet. When people get old, cold comes from their feet, so it is also for the purpose of health preservation to warm their feet with a hot kang. People need a clear head and are not afraid of cold, so they sleep on the kang, with their heads facing outwards and their feet facing inwards. This is based on science.
If you sleep upside down, it's called "head in".
In addition, many kangs are slightly higher outside than inside, so their heads are high and their feet are low. In addition, the kang edge is in the middle of the house, with good air circulation, lukewarm and moderate. Either the fire wall inside the kang is extremely hot, or it leans against the window and is easily blown away by the wind.