How Do Steam Boilers Work?

Written by :
Last updated: October 31, 2023

Boilers or steam generators are closed, cylindrical vessels that create steam by applying heat energy to water. Amazingly, these devices have been around for over 200 years. Steam boiling units are usually found in older residential homes or industrial settings and operate at higher temperatures than their hot-water boiler counterparts. Since they can be very costly to replace, it is well worth ensuring that these units are well maintained all year long. While they are durable, it’s well worth consulting the professionals regularly and fixing any issues as they arise.

Much like hot-water systems, a steam boiler also distributes energy to various radiators in the home. However, rather than using hot water to do so, it uses steam – hence the name steam boiler.

Steam-fuelled radiators are often bulkier than those that are powered by water and are often seen in old apartment buildings. Steam-powered boilers have certainly stood the test of time and are durable devices. However, like any other heating device, they should be serviced regularly to avoid potential problems and breakdowns.

Let’s explore how they work, the heat transfer process, and the differences between types of units available for homeowners.

What is a Steam Boiler?

Steam boilers are essentially a heating technology vessel that uses steam to heat your home or building. Steam boiling units usually come in two primary designs, namely the water tube boiler and the flame or fire tube boiler. So, what differentiates these boiler systems?

Water tube steam boilers have special tubes that contain water. These water-filled tubes are encompassed by hot gas. In a flame tube system, hot gas flows within the tubes and these tubes are surrounded by water.

Water tube systems are usually used in industrial settings as they can withstand huge pressure of up to 200 bar. Flame tube boilers, on the other hand, can withstand pressure up to 25 bar.

How Is Steam Produced In a Boiler?

Steam boilers are cylindrical in shape and usually stand horizontally. These cat-iron structures are usually filled with 50 – 75 % water and have a gap that allows for steam production. They work via high pressure and turn water into steam. This steam then heats the radiators in a building or home via connected tubes.

A specialised burner beneath the tank heats up the water and transforms it into steam. Since hot air rises, the steam heads upwards and reaches various supply pipes. These pipes connect to different radiators in the home or building. Once the steam reaches the radiators, it begins to condense and eventually turns back into water. Once this occurs, the water travels back to the cast-iron tank, and the process is repeated.

Home steam boilers are usually a one-pipe or two-pipe system and you can easily see what time of system you have by looking at your radiator and counting how many connecting tubes it has. One pipe systems deliver steam to the radiator and water back to the boiler with the same tube, whereas 2-pipe systems have two separate ones, one for steam and one for water. Both types of boilers utilise air vents. The air pushes through the system and enables the steam to enter the central heating system.

Unfortunately, impurities in the water supply can lead to Total Dissolved Solids (TDS) in the boiler system and this is when water treatment solutions become critical. Over time, these impurities can impact the ability of the boiler to generate steam and feed the central heating system. To prevent a build-up of dissolved solids, you can use water softeners, a reverse osmosis filter, or a specialised demineraliser. These water treatment solutions can go a long way in enhancing the life of your steam boiler. Ultimately, when boiler water is void of these impurities, the system will work better. Water treatment options can be easily done at home.

Popular Features of a Steam boiler

Steam boilers have several important features to ensure they power the heat source and circulate the desired temperature throughout your home. Many of these features work to protect the boiler from potential damage. Important features include:

Regulator or pressure gauge:

This ensures that your steam boiler is operating at optimal pressure. If pressure levels get too high, this system automatically switches off the fuel supply. This automatic system effectively controls pressure levels to ensure optimal functioning.

Pressure relief/temperature valve:

This is a backup to the regulator and kicks in if the pressure gauge fails to cut the fuel supply. If the boiler reaches a dangerous pressure level, this function will release steam to reduce the pressure.

Sight glass:

This glass piece of equipment shows the current water level and allows boiler-owners to see if there is enough water (or too much) in the system.

Water cut-off:

If the water in the boiler drops below a certain level, this control will turn the system off, to avoid damage.

How Long Does a Steam Boiler Last?

Luckily, most steam boiler systems are built with durability in mind. Most units, if well maintained can last for between 15 and 30 years, and some have even lasted much longer. However, this is due to brilliant maintenance. By spending a little each year and ensuring the unit is maintained, you can ensure it lasts for many years and avoid a costly replacement.

Maintenance of a Steam Boiler

If you have a steam boiler at home, you will want to check those water levels regularly to ensure that they haven’t dropped. A lack of water or too much water within the boiler can cause problems.

You will also need to check the build-up of sediments in the water and pt for a water treatment solution if needed. While homeowners can do this themselves, it is important to get a professional in before the colder, winter months.

A yearly check will ensure that everything is operating as it should and will prevent the need for costly repairs or replacements that result from neglecting maintenance.

Related Post: 5 Ways to Prepare Your Boiler For Winter


While not all homes, and especially modern homes, have a steam boiler, they are still popular devices, and for excellent reason. They work well, generate great heat, can last for many years, and can effectively heat an entire home. Unfortunately, completely replacing a central heating operation is a costly endeavour, so if your steam boiler is still working optimally, it is best to maintain it. With excellent maintenance, it could easily last you a good number of years.

Do you have one of these units? If so, what has your experience been? Let us know!