Is the heating steam? Or heating water? Why do you always say; Heating uses steam to provide heating!

Generally, the water in the heating system is heated by steam, and then hot water is circulated to all households to release heat, and the released heat is recovered to continue heating. In the past, steam was used to keep warm. The method is to release steam directly into the indoor radiator. Steam liquefies when it meets a cold radiator, which instantly increases the temperature of the radiator. The advantage is that the room temperature rises rapidly (the steam temperature is higher than 100℃), and the disadvantage is that it is dangerous and easy to leak water. It's not usually used now.