Fire (huo) is one of the Wu Xing, the five phases of Chinese cosmology. It is the phase of heat, brightness, and upward, outward movement, associated in the classical correspondences with the direction south, the colour red, the season of summer, the emotion of joy, and the bitter taste. In the generating cycle (sheng) Fire produces Earth, its ashes enriching the ground; in the controlling cycle (ke) Fire restrains Metal, melting and reshaping it. These cycles of mutual generation and control order the relations among the five phases and underlie their application in Chinese medicine, the almanac, feng shui, and the art of fate calculation. These are the conventions of the Chinese cosmological tradition, in which the five phases are woven into a broad system of correspondence linking directions, seasons, organs, colours, tastes, and emotions.
Fire follows Wood in the generating cycle (Sheng) because wood burns and produces flame, and it generates Earth in turn, since ash returns to soil. In the controlling cycle (Ke), Fire melts Metal, while Water controls Fire by quenching it. The Han-dynasty correlative system set out in texts such as the Huangdi Neijing assigns Fire to the heart and small intestine, the bitter taste, the colour red, the direction south, and the season of summer, and it associates the phase with joy in excess and with the spirit or shen said to reside in the heart. In four pillars (BaZi) astrology a chart dominated by Fire is read as ardent and expressive but prone to burning out without the moderating check of Water.
Sources Science and Civilisation in China, Volume 2: History of Scientific ThoughtJoseph Needham with Huangdi Neijing (The Yellow Emperor's Inner Classic)Traditionally attributed to Huangdi; actual authorship unknown, Chinese Mathematical Astrology: Reaching Out to the StarsHo Peng Yoke