Types of boilers and their evolution throughout history

The history of boilers

During the Industrial Revolution, a period marked by rapid successive inventions where new machinery appeared daily, Scottish engineer James Watt developed the first steam engine.

However, Watt did not start from scratch. At the beginning of the previous century, French physicist Denis Papin designed a machine capable of storing water, heating it, and generating steam. The so-called ‘Marmite’ could hold up to 150 litres of water and featured a valve to regulate steam pressure. The modern pressure cooker is a descendant of this invention, which eventually inspired various types of boilers.

During the height of Britain's industrial boom, steam was used to power larger machines in the emerging factories. It also made it possible to transport the raw materials they required and export goods worldwide using steam-powered railways and ships. Passenger transportation followed the same path, eventually paving the way for heating homes in cities.

Perhaps the most iconic example of the use of steam boilers in homes can still be found today in New York City. The well-known image often seen in films, with white steam rising from manholes, is closely linked to the steam used to heat the city’s oldest buildings.

Coal-fired boilers, some of which are still in operation today, were installed in other early 20th-century buildings. Pipes carried hot water to homes, distributing it through cast iron radiators. However, the further the water travelled from the boiler, the cooler it became. This required heating the water to higher temperatures, causing residents on lower floors to endure excessive heat so that those in upper-floor apartments could keep their homes warm—an issue that continues to affect most centralised water-heating systems today.

Gas boilers: early days

The shift to gas boilers meant a radical change for both urban and rural areas. This new method of heating water in so-called atmospheric boilers relied on a series of gas-powered burners to heat a coil through which water circulated until it reached 90 °C. Butane cylinders reached their peak popularity in the 1960s and 1970s, when they served a rapidly growing population.

However, the term ‘atmospheric’ carried a significant drawback: the combustion chamber was exposed to the surrounding air. This allowed carbon monoxide to seep into the area where the boiler was installed. Another downside of these boilers was their low energy efficiency, of around 75% compared to modern systems.

To address these shortcomings, sealed-system boilers were introduced. These boilers, named for their enclosed combustion chamber, improved efficiency by about 10% over atmospheric models. A distinctive feature of this type of boiler is its need for an air inlet and gas outlet. This is accomplished through two pipes that act as a chimney.

Condensing boilers: more efficient and environmentally friendly

Gas boilers underwent a major innovation with the introduction of condensing boilers. This type of boiler includes a second coil to preheat water using the gases produced during combustion. The steam reaches this second coil at 150 °C and condenses, heating the water to 70 °C. This preheating reduces the amount of fuel needed to finish heating the water. The water resulting from condensation must be drained through an outlet.

Condensing boilers are used to distribute heat via radiators or underfloor heating. Their only drawback is the higher installation cost compared to the previously mentioned models. Still, their superior efficiency compared to older models does lead to reductions in gas bills in the long term.

Thanks to their energy efficiency—exceeding 100%—and their lower environmental impact, condensing boilers have been the only type allowed for manufacturing since the adoption of a European Directive in September 2015. As a result, atmospheric and sealed-system boilers are no longer installed today.

Forced-draft boilers and low-NOx boilers

Other types of boilers have also fallen out of use. Forced-draft boilers (similar to atmospheric boilers but equipped with a fan) and low-NO_x boilers (similar to sealed-system boilers but less polluting and slightly more efficient) are no longer manufactured either.

Diesel and electric boilers

By contrast, diesel boilers are still commonly used in single-family homes, whereas in large cities, natural gas has largely replaced butane gas. Electricity is also a key resource for generating domestic heat. However, household budgets often lead families to choose more affordable energy sources for heating their homes or domestic water, despite the narrowing price gap.

Upgrading domestic boiler installations is becoming increasingly common, while several autonomous communities offer programmes to replace outdated boilers with newer, more advanced models. The goal is to continue improving energy efficiency, enabling families to enjoy more affordable heating while making it more environmentally friendly.

For this reason, in addition to investing in new, energy-efficient equipment, proper maintenance is also essential to ensure optimal performance. If you have a gas boiler, Endesa offers a Comprehensive Gas Maintenance service, so you can rely on us for any repairs your boiler or heating system needs, as well as for regular inspections. You’ll be able to enjoy your home like never before, with a comfortable temperature and zero worries about maintaining your boiler.