White snow, descending like broken jade, covers the red walls. After a snow day in the cold winter season, the Palace Museum looks extraordinarily beautiful and frigid. According to some historical materials, China once experienced extremely cold weathers during the Ming and Qing dynasties, which witnessed temperature dropped to 20 or 30 Celsius degree below zero. 

Today, when on a tour of the Palace Museum, we can see warm housesadjacent to some halls. For example, the Yangxin Hall has a warm house called DongnuanGe, where emperors used to hold the First Writing Ceremony on the New Year day. Where did the name "warm house" come from then? The answer has something to do with the heating system in the royal palace: the underfloor heating. Royal servants built a brick-made circuit flue beneath the floor. The fireplace, installed outside, burns coal and produces heat that will warm up the floor inside the hall. The heat will ascend from the beneath and reach out to every room through the underfloor circuit flue. The circulation of heat will raise the temperature indoors and help people fend off the coldness as a result. Since the fireplace and chimney got installed outside, this heating system can avoid polluting the air indoors. It is safe, clean, and effective.

According to some archaeological surveys, the underfloor heating system has existed in China for more than 1000 years. The materials and design of the underfloor heating system were highly standardized during the Ming and Qing dynasties. The royal court even established an ad hoc organization charged with heating-related issues during the winter season. Yangxin Hall of the Palace Museum received a massive renovation this September. When the workers dug out the floor bricks of the hall, a sophisticated underfloor heating system surfaced for the first time. Everyone marveled at it.

Apart from the underfloor heating system, royal members also used the charcoal braziers indoors. Bronze and cloisonne braziers are particularly elegant and cherished. People put the burning charcoal into the brazier and then covered it with an engraved mantle. Such a brazier was both warm and eye-catching. To be sure, charcoal braziers are not problem-free: the burning charcoal could result in gas poisoning or fire if improperly handled. That is why the royal families were very cautious when using the charcoal braziers and they asked specialized personnel to take care of them.

The Palace Museum witnessed over 600 years of history. Every brick and tile here has some untold stories. Every hall and building mirrors the wisdom of the ancient Chinese. All these secrets are awaiting explorations by later generations.