A boiler is defined as “a closed vessel in which water or other liquid is heated, steam or vapor is generated, steam is superheated, or any combination thereof, under pressure or vacuum, for use external to itself, by the direct application of energy from the combustion of fuels, from electricity or nuclear energy.”

A boiler is comprised of a separate container called burner, which is attached to it. The steam needed to heat homes, buildings and other structures are created by the fuel that is burned and supplied to the boiler from the burner. Natural gas is released into the boiler through a special pipe, a tank that is pressurized is used to supply the oil while the wood pellets are propelled into the burner. These fuels interact with air and are burned in order to provide the necessary heat needed to convert water into steam.

Once the fuel is supplied to the burner and heated up to the required point, the gases or the fire from the fuel is directly released into the boiler to heat up the water. This can happen in one of the two ways depending on the type of boiler used.


There are mainly two types of boilers that work in different ways to produce heat.

Fire Tube Boilers

The most commonly used are fire tube or shell boilers. In fire tube boilers the fire or hot gases released from the burner are run through within the tubes inside the shell of the boiler with water surrounding them. The tubes are set in banks in order to let the gases go through the boiler four times before letting out the stack. The fire tube boiler systems can release up to 25,000lbs or 750hp of steam per hour. About 80% of the boilers that are in use today belong to this particular category.

Must read – How Exactly Does A Fire Tube Boiler Operate?

A subtype of this boiler is the packaged boiler, shipped complete with fuel burning equipment, mechanical draft equipment, automatic controls, and accessories and is designed to function automatically with a very minimum of attention. It is particularly important to prevent scale formation in this type of boiler.

Water Tube Boilers

The fuel or hot gases are released on to and the area around the outer surface of tubes filled with water. The tubes are vertically arranged in the shell. Water tube boilers are generally built in the rectangular shape with two or three drums. While the top drum is used for separating water and steam, the bottom drum is used to collect the sludge. They are usually utilized when more than 750hp of steam per hour is required.

Also, read – Advantages and Working Principle of Water Tube Boiler

The fuel or hot gases released into the boiler from the burner heats up the water causing the temperature to rise up to 212 degrees Fahrenheit. That is when the steam is formed. The steam generated is then circulated throughout the building or home using radiators, vents, and pipes, specifically created for heat transfer.

Some of the heat is retained in the boiler as the heat required for keeping the building or home warm needs to be regulated, or else they will get overheated. Since more steam is produced as the temperature increases, it is essential to check the boiler and ensure that excess pressure is not built. To check the pressure build up, run your boiler for short duration of time. Furthermore, they have to be maintained regularly to keep them in optimum working condition.