James Elston

Published April 8, 2024

A condensing boiler is the cream of the crop when it comes to keeping your central heating system in good shape. These boilers maximise energy efficiency by using “condensing” technology.

In other words, they use less energy, produce less carbon dioxide (CO2), and are less costly to run compared to traditional boilers.

They’re so great, in fact, that since 2005, building regulations have forbidden the installation of new non-condensing boilers! This step towards modern condensing boilers is part of the UK’s greener future campaign to achieve net-zero carbon emissions by 2050.

We’re excited to tell you all about condensing boilers, from the flue gas recovery system, waste gases, and condensate pipe to their efficiency and beyond. We’ll even throw in a few boiler efficiency tips too!

The best news? If you keep your condensing boiler safe and well-maintained, it could last 15 years!

What Is A Condensing Boiler?

A condensing boiler represents the latest advancements in boiler technology, unlike standard models from yesteryear. They’re designed to capture and reuse “lost heat” to keep pipes and unused water in the system warm until needed. The process of condensing water vapour (steam) and exhaust gases back into water is called condensing technology.

Traditionally in non-condensing boiler types, heat would be lost through the chimney or evaporate into the atmosphere.

A condensing boiler is an energy-efficient home heating system that you should consider installing.

How Do Condensing Boilers Work?


Condensing boilers and non-condensing boilers are similar in terms of combustion. In other words, burning fuels like gas or oil generates heat. The domestic boiler’s heat exchanger uses this energy to heat and transfer water throughout the boiler system.

Non-condensing models lose about 30% of heat during this process while condensing types only lose around 8% to 10%.

Heat recovery

A condensing boiler uses one of two ways to improve its efficiency regarding heat recovery. However, non-condensing boilers do NOT have these features.

  1. A condensing boiler captures heat that is lost from flue gases (exhaust or stack gases) via the secondary heat exchanger. This is found very close to the flue pipe exit point.
  2. The flue gas recovery system optimises the flow rate and allows flue gases to heat cooler pipes, reducing the energy (fuel) needed to heat our systems.

The captured heat – called latent heat – allows these boilers to achieve over 90% efficiency, leading to a mega carbon footprint reduction! Also, lower temperatures improve the condensation process which leads to more heat recovery.

Either way, you’re getting more heat and energy for the same amount of money!

Understanding efficiency ratings

Understanding efficiency ratings is key to recognising the value of condensing boilers in terms of energy savings and boiler lifespan expectations. These ratings show how well the condensing boiler converts fuel to heat and are shown as percentages.

  • Modern condensing boilers are efficient models, with a 90% energy rating.
  • Older boilers are less economical, with only 70- 80% efficiency.

A high-efficiency rating indicates more heat is produced and offers fantastic energy-saving heating solutions. If you want maximum efficiency, maintain an optimal temperature between 60 °C and 65 °C.


Higher energy ratings have a direct impact on the lifespan of your condensing boiler. Condensing models, including a combi boiler and gas condensing boiler, operate less to produce the same amount of heat, reducing wear and tear over time. Maintenance and service checks by heating experts should be done at least once a year to keep your central heating and boiler systems in good health. Check out our guide to learn more about how often a boiler should be serviced.

Types Of Boilers: Explained

When considering condensing boiler options, understanding the differences between boiler types is important.

Choosing the right boiler size should be based on your specific household’s needs. Opting for units that are too small can result in a limited hot water supply while choosing one that is too big can result in wasted heat and money!

Combi boiler

Ever asked yourself what the difference is between a condensing boiler vs combi boiler? Aren’t they the same thing?

A combination boiler (or combi boiler for short) is a type of condensing boiler. They are popular options for many households.

A combi boiler combines the features of highly efficient boilers and central heating systems in one compact unit. It doesn’t need a separate water storage tank. They are ideal space-saving options, particularly in smaller homes.

Combi boilers require one of four additional requirements for installation, namely:

  • Load compensation
  • Weather compensation
  • Smart controls
  • Passive Flue Gas Heat Recovery Device (PFGHRD)

Best condensing boiler types:

An average a three-bedroom home typically requires a condensing boiler unit with a power outlet of 20 – 30 kW.

  • Best small condensing combi boiler – Viessmann Vitodens 100 w (26 kW)
  • Best large condensing combi boiler – Worcester Bosch Greenstar CDi Classic (38 kW)

System boiler

System boilers, unlike combi boilers, require a separate hot water cylinder for storage, making them less space-savvy. They are ideal for larger homes with multiple bathrooms or higher hot water demands. The separate tank allows them to supply hot water to many taps simultaneously.

Heat-only boiler

Also known as conventional or standard boilers, heat-only boilers are often found in older homes. They are the bulkiest boiler of the three and need space for a hot water cylinder and a cold water tank. These tanks are usually stored in the loft. These are ideal for older homes with traditional heating and hot water systems.

Popular boiler brands

Here are a few reputable brands that Eco Happy can recommend:

  1. Worcester Bosch
  2. Vaillant
  3. Baxi
  4. Viessmann
  5. Ideal
  6. Alpha

Benefits Of Condensing Boilers

Upgrading boiler benefits for homeowners transcends to:

  • Require less fuel: Modern condensing boilers use less fuel to produce heat, giving you more bang for your buck.
  • Lower energy bills: Energy-savvy boilers can reduce energy bills, potentially saving you up to £300 per year.
  • Connect to smart thermostats: When a condensing boiler is connected to smart thermostats or radiator valves, your energy bills can be further reduced.
  • Green standards: A-rated condensing combi boilers emit lower carbon emissions, aligning with green standards.
  • Eco-friendly: Trading in your older boiler for a modern combi boiler can reduce your carbon footprint by 1,220 kg of CO2 per year!
  • Long lifespan: Well-maintained condensing boiler systems can last 15 years with minimal breakdowns or repairs.

Safety And Reliability

When gas condensing boilers – or any condensing boiler for that matter – became standard in 2005, there were a few concerns that came about. These included:

  • Early corrosion
  • Over-priced
  • Trapped water in the boiler unit
  • Unreliable boiler technology
  • Dangerous flue and plumbing
  • Dampness issues

Now, some 18 years later, the condensing boiler has made a significant turnaround. They are safe, reliable, highly valued and highly efficient.

Boiler technology, such as water vapour condensation, has boosted efficiency and gets our stamp of approval.


What is the difference between a condensing boiler and a standard boiler?

A standard boiler and a condensing boiler work in a similar way as they both burn fuel to generate heat. The difference lies in their efficiency: condensing models are 90% efficient as opposed to 70-80% in standard types.

Where the confusion may come in is that all modern boilers installed after 2005 are “standard” condensing boilers, due to Boiler Plus regulations.

The difference between combi boilers and condensing boilers

A combi boiler is a type of condensing boiler – there are ultimately no differences. They both provide heating and hot water to our homes through the condensation process, and neither requires a separate water storage tank.

How do I know if my boiler is condensing or non-condensing?

One way to check if your boiler is condensing or non-condensing is to check if the boiler unit has a condensate pipe. But, what is a condensate pipe? This pipe is located at the back of the boiler unit and clears your heating system of acidic wastewater formed by waste gases. These CO2 and water vapour byproducts drain into the sewer via the condensate pipe.


A condensing boiler represents a significant leap in boiler efficiency and eco-friendliness. Their ability to minimise energy consumption and lower heating bills not only provides environmental benefits but also offers tangible rewards for homeowners.

By using advanced boiler technology, these units give you more bang for your buck in terms of heating output and running costs. The 2005 shift towards these modern boilers marked an era of the UK’s commitment to a greener future.

If you’d like to know more, chat with the Eco Happy team today.

James Elston

Boiler Expert

James Elston is the top boiler replacement and heating expert at Eco Happy. He has over 20 years of experience in the industry, focusing on Gas Safe boiler installations and offering home-heating and energy-saving solutions to homeowners across the UK. From sourcing the most energy-efficient combi boiler to providing specialist heating advice, James ensures that Eco Happy maintains the highest standards and best customer service.

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