How to keep warm in ancient times: During the Ming and Qing Dynasties, there were fire paths under the floor tiles of many palaces, and there were fixed fire sites. After the fire, hot air spreads to the whole floor of the room along the fire path, which is the embryonic form of local heating.

The principle of modern floor heating is similar to this. However, this luxurious earthworm is only available in royal or aristocratic families, and ordinary people may not have seen it.

People in the north use kang, which not only has a long history, but also is widely used in rural areas. Make a stove in the room or yard and make a fire under it. The stove is connected with the kang through the flue, and hot air or flue gas diffuses into the kang along the flue to warm the kang. People sleep, eat, read and entertain guests on the kang, and they don't feel cold at all. This principle is basically the same as floor heating. But also conforms to the hygienic habit of people with cold head and hot feet, and is environmentally friendly and warm.