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Unlocking the Energy-Saving Secrets: What Is a Condensing Boiler?

Understanding the different boiler types can be pretty confusing. Presently, the focus is on condensing boilers. UK building rules now mandate that any new boiler installation should be a condensing model. So, what distinguishes these boilers, and how do they vary from conventional boilers?


In this article, you will learn what a condensing boiler is, how it works, and how it differs from a non-condensing one.


Unlocking the Energy-Saving Secrets: What Is a Condensing Boiler?

What Is A Condensing Boiler?


A condensing boiler is a central heating system that employs condensing mechanisms to enhance energy efficiency. In contrast to conventional non-condensing boilers, these are built to capture the latent heat from the steam produced during combustion.


This condensation technique enables the boiler to extract more heat from its fuel, boosting its overall effectiveness. As a result, they have an efficiency rating exceeding 90%, while traditional non-condensing boilers typically land efficiency ratings of 70% to 80%.


Such superior efficiency translates to decreased energy use and diminished fuel expenses.


Due to their heightened energy efficiency and ecological advantages, many nations now prefer condensing boilers for new setups and boiler replacements. Their top-tier efficiency and environmental positives have elevated their demand throughout Europe, especially in the UK.


Here, government incentives like the ECO4 scheme encourage households to opt for condensing boiler installations.


Is Condensing The Same As Combination Boiler?


Many individuals mix up condensing boilers with combination boilers. While it's true that combi boilers can be condensing, it's also crucial to understand that not all condensing boilers fall under the combination category.


For example, a combi boiler:

  • Eliminates the need for a separate hot water tank.

  • Provides hot water instantly to both radiators and taps. On the other hand, traditional boilers rely on an independent hot water tank to store pre-warmed water, requiring additional space for its placement.

Combi boilers are more compact and are well-suited for smaller households, offering on-the-spot hot water. Owing to these features, they have quickly become the top choice for many UK households. However, for larger residences or those with several bathrooms, a conventional boiler paired with a hot water tank might be a better choice to handle the demand.


Fortunately, whether you're considering a combi or a traditional boiler, you can choose a condensing version. This allows anyone to pick an energy-efficient boiler tailored to their needs, ensuring an A-rated unit's benefits.


What Does Condensing Mean?


Condensation involves converting a substance from its gaseous form to its liquid state. In boilers, condensation refers to transforming water vapour, a by-product of combustion.


When a boiler burns fuel, it emits hot combustion gases and produces water vapour. In a condensing boiler, these hot gases and vapour are directed through a secondary heat exchanger tailored for condensation. As the steam meets the cooler surface of this exchanger, it releases its latent heat and turns back into liquid.


The essential advantage of this condensation in a condensing boiler is the ability to capture and utilize the extra heat that would otherwise be lost in conventional boilers.


How Does A Condensation Boiler Work?


A condensing boiler uses condensing technology to capture and capture the latent heat from the steam generated during fuel combustion.


Here's a simplified breakdown of a condensing boiler's operation:

  1. Fuel Burning: The boiler ignites fuel within a combustion chamber, gas or oil. This combustion produces heat and results in hot gases, with water vapour being a significant by-product.

  2. Primary Heat Transfer: These hot gases and water vapour travel through a primary heat exchanger. This metallic component facilitates heat transfer from the gases to the system's circulating water. Consequently, the water's temperature rises.

  3. Condensation Process: The gases, still holding onto some heat and water vapour, proceed to a secondary heat exchanger designed for condensation. This exchanger is typically made from materials that resist corrosion, given the acidic qualities of the condensation by-product.

  4. Capturing Latent Heat: As the water vapour makes contact with the cooler surface of the secondary heat exchanger, it condenses, releasing its latent heat. This is the energy within the vapour typically lost in non-condensing systems. The heat exchanger ensures the circulating water absorbs this additional warmth, further elevating its temperature.

  5. Emission of Flue Gas: Having transferred most of their heat and moisture, the cooled gases are channelled out of the boiler via a flue. The by-product of the condensation, a liquid termed 'condensate', is gathered and drained from the boiler.

  6. Distribution in the Heating System: The now enriched hot water, having absorbed heat from both combustion and condensation, circulates within the heating infrastructure. It can then be directed for central heating, such as through radiators or underfloor heating, or be used as domestic hot water.

Advantages Of A Condensation Boiler


Condensing boilers offer homeowners three primary advantages:


Enhanced Energy Efficiency for Your Home


Older boilers, especially those over a decade old, might only achieve efficiencies around 60%. Upgrading to a condensing boiler can boost this efficiency by up to 30%.


Cost Savings


As stated by the Sustainable Energy Authority of Ireland, homeowners can reduce their energy expenses by as much as 20% when transitioning to a high-efficiency condensing boiler with the appropriate controls.


Diminished Carbon Emissions


Commit to a greener environment! Condensing boilers emit notably fewer carbon emissions compared to their traditional counterparts.


What Is A Non-Condensing Boiler?


A non-condensing boiler is a central heating system lacking condensing capabilities.

Fueled by either gas or oil, this boiler type heats water, distributed through radiators or underfloor heating, offering warmth throughout a building. Once the water cools, it circulates back to the boiler to be reheated, perpetuating the heating cycle.


These systems come equipped with a flue, serving as an outlet for waste gases produced during the combustion process.


As these boilers operate, they produce both gases and water vapour. However, unlike their condensing counterparts, non-condensing boilers release these gases and vapour without turning the latter into liquid, leading to a significant heat loss in the emitted water vapour.


Before the early 2000s, non-condensing boilers were commonplace in the UK. However, with condensing boilers' features and growing popularity, they gradually became the norm for central heating setups.


How Does A Non-Condensation Boiler Work?


Unlike a condensing boiler, a non-condensing boiler operates in a more straightforward manner. Here's an overview of its operation:

  1. Combustion: Inside the combustion chamber, the boiler ignites the fuel, creating a flame that yields heat.

  2. Heat Transfer: The combustion yields hot gases, which are then channelled through a heat exchanger. Here, the heat from these gases is transferred to the circulating water, warming it up.

  3. Emission of Flue Gas: Once they have travelled through the heat exchanger, the combustion gases, including the water vapour formed during combustion, are expelled outside the building via the flue.

  4. Distribution in the Heating System: The now-warmed water circulates within the heating infrastructure, travelling through pipes to radiators or underfloor heating systems and distributing heat throughout the premises.

  5. Re-circulation of Cooled Water: After dispersing its warmth, the water returns to the boiler via a return line. Once back, it's reheated and sent out again, thus completing a heating cycle.

A key distinction of non-condensing boilers is that the water vapour created during combustion is mixed with other waste gases and isn't condensed back into a liquid state.


This implies that the intrinsic latent heat within this vapour isn't captured or used. Consequently, non-condensing boilers only partially exploit the heat energy from the burned fuel, making them less energy-efficient than their condensing counterparts.


Condensing Vs. Non-Condensing Boilers- What's The Difference?


In straightforward terms, condensing boilers boast superior energy efficiency. This translates to significant savings on yearly energy expenses, with some reports indicating up to 30% reductions.


Beyond just cost savings, condensing boilers have a more eco-friendly profile compared to their non-condensing counterparts. Their enhanced efficiency results in reduced waste and lower fuel usage, significantly reducing your environmental impact.


Additionally, they offer a more uniform and precise approach to heating structures. Their ability to modulate output based on heating needs ensures the delivered warmth aligns perfectly with the building's demands.


How Long Does A Condensation Boiler Last?


The lifespan of a condensing boiler will vary on its build quality, model and usage. However, you can prolong the lifespan of a condensing boiler through correct servicing. Servicing of your boiler should be done once a year by a Gas Safe registered heating engineer.


Always check your boiler's warranty to ensure you choose a quality option.


Are All New Boilers Condensing Ones?


From 1st April 2005 onwards, it became a legal requirement in the UK for all newly installed gas boilers to be of the condensing type. This mandate was extended to oil boilers starting from 1st April 2007. Since around 40% of UK emissions are attributed to residential sources, these regulations were introduced to address climate change.


What Size Boiler Is Perfect For Me?


The capacity of a condensing boiler is gauged in terms of its kilowatt (kW) output. The boiler's size depends on factors such as the number of bathrooms, radiators, and the overall usage in a home. Typically, a house with 2-3 bedrooms and a single bathroom might have a condensing boiler ranging between 23-30 kW in output.


Are The Emissions From Condensing Boilers Dangerous?


In brief, they can be hazardous and should not be breathed in. Ensuring your boiler's exhaust gases are directed to a safe area is crucial. This is why boiler flues are designed to lead outside the house through a wall or roof, running waste gases and condensation away from indoor spaces.


It's also wise to have a carbon monoxide detector in your home. Should carbon monoxide be present, the alarm will activate, much like how a smoke detector functions.


Read more: Cavity Wall Insulation Pros and Cons


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