What is a Boiler and How Does It Work?

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How Does a Boiler Work?


A boiler is water containing vessel which transfers heat from a fuel source (oil, gas, coal) into steam which is piped to a point where it can be used to run production equipment, to sterilize, provide heat, to steam-clean, etc.

The energy given up by the steam is sufficient to convert it back into the form of water. When 100% of the steam produced is returned to be reused, the system is called a closed system. Examples of closed systems are closed steam heating, hot water heating, and “one-pipe” systems.

Since some processes can contaminate the steam, so it is not always desirable to feed the condensate back into the boiler. A system that does not return the condensate is called an open system.

The two main types of boilers are:

  • Firetube – the fire or hot gases are directed through the inside of tubes within the boiler shell, which are surrounded by water. The tubes are arranged in banks so that the gases can be passed through the boiler up to 4 times before passing out the stack. This system exposes the maximum heat transfer surface to the water. Firetube boilers are also known as shell boilers and can produce up to approximately 750 hp or 25,000 lbs of steam per hour. 80% of boilers in use are of this configuration.

  • 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.

  • Watertube – the fire or hot gases are directed to and around the outside of tubes containing water, arranged in a vertical position. Watertube boilers are usually rectangular in shape and have two or more drums. The separation of steam and water takes place in the top drum, while the bottom drum serves as a collection point for sludge. This system is usually used when more than 750 hp or several hundred thousand lbs of steam per hour, are needed.

  • There are other designs with special configurations, adapting them to particular applications.

Further Reading

How Often Should You Have Your Furnace Serviced?

Are Smart Thermostats Worth It?

How do I Convert My House to Natural Gas?

What are the Advantages and Disadvantages of Heat Pumps?

For professional HVAC services, call Celestial Air today at (973) 627-4899.