The two general categories of boilers are hot water and steam boilers. Most small commercial buildings, manufacturers, and even some food processors use hot water boilers. Water is heated to appropriate distribution temperatures, typically 140-180 F, and usually returned about 20 F lower temperature for reheat. Where applicable, hot water boilers are preferred because they normally do not need operators or special water chemistry. Further, since they operate at lower temperatures, hot water boilers can operate at higher fuel conversion efficiencies than steam boilers.
Some boilers heat the steam even hotter than the boiling point temperature.
This is referred to as superheated steam. And Furthermore . . .