Boiler is a closed vessel where heat is generated by the combustion of fuel. The classification of boilers is based on several factors and is classified into six categories: According to the contents of the tubes, the number of tubes, the position of the furnace, the axis of the shell, methods of circulation of water and steam, and the use.

The term "kilowatt" is used by heating professionals to describe how much heat energy your boiler produces. According to the general kW rule, you will need a higher kW boiler the more heat and hot water you need for your home.

In a fire-tube boiler, hot gases from a fire travel through one or more tubes that run through a sealed container of water.

The boiler efficiency formula is given as \(\eta = \frac{Energy / Output}{Energy / Input} \times 100\).

In a high-pressure water tube boiler, water passes through tubes that have been heated externally by the fire. The heat from the fire is transferred to the water which is converted into steam to be sent into the next steps to generate power.