Principle of Operation for Gas-Fired Boilers:

Water inside the boiler (shell) is continuously heated by the energy released from the combustion of gas fuel in the furnace, causing its temperature to rise and produce pressurized steam. As water's boiling point increases with pressure, the sealed boiler restricts the expansion of steam, creating pressure and forming thermal energy (strictly speaking, the steam in the boiler is formed by the water being heated to saturation pressure in the shell and then vaporizing). As a widely used energy source, it is extensively utilized.