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Last updated: 22nd February, 2024


Condensing vs Combi Boilers

Condensing vs Combi Boilers

In this guide, we’re going to be explaining what each of these terms mean so you know exactly what it is you need to be looking for when choosing your new boiler.

When shopping for the right boiler for your home, you may be confused by the different types, names and terms, such as condensing, combi, system and conventional boilers.

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What is a Condensing Boiler?

Condensing boilers are gas or oil-fired boilers designed for more efficient heating.

When a boiler burns fuel, it produces water vapour (steam) which contains heat.

This water vapour has the potential to contribute to the heating of the home; however, until condensing boilers were developed, the vapour went straight out of the flue pipe.

This meant that up to 30% of the heat produced by the boiler was being wasted, and the boiler would need to use more fuel to make up for the loss, resulting in high energy bills.

Condensing boilers were developed to stop this waste.

How Does a Condensing Boiler Work?

Condensing boilers use a ‘Flue Gas Recovery System’ to recycle the heat from the steam and prevent it from being lost.

The system includes two heat exchangers.

The water enters the condensing chamber first, picking up latent heat from the hot flue gases as they cool.

The moisture in these gases then condenses into droplets at the heat exchanger's bottom.

The condensation droplets are then expelled to the drain while the heated water enters the primary heat exchanger to collect more heat before finally flowing to the radiators and hot water taps.

This results in a more efficient heating system and much lower energy bills. 

What is a Combi Boiler?

A combi boiler, short for combination boiler, combines a water heating system and central heating unit into a single body, handling heating and hot water without needing separate hot and cold water tanks.

How Do Combi Boilers Work?

Regular boilers are fed cold water from a cold water tank, which is often stored in the attic. This is then warmed by the heat exchanged in the boiler and stored in a hot water cylinder where it is stored until you need it.

A combi boiler, however, is fed cold water directly from the mains and can provide hot water instantly without the need to store hot water in a cylinder..

This means you can get hot water on demand and won't run out like it does with other boilers, as well as additional space in your home without the need for additional cylinders.

Is a Condensing Boiler the Same as a Combi Boiler?

Yes and no. A combi boiler is a type of condensing boiler.

All modern domestic boilers, including combi boilers, system and regular boilers use condensing technology to make them more energy efficient. 

So when it comes to choosing the right boiler for your home, you don’t need to choose between a combi boiler and conventional boiler as all combis are condensing. 

How to Choose Between a Combi, System and Regular Boiler?

Choosing the right condensing boiler from your home can be a tricky decision, however, certain boiler types suit certain types of homes more than others.

Is a Combi Boiler Suitable for My Home?

Combi boilers are typically best suited to small to medium sized homes with a low demand for heating and hot water at any one time.

They’re also ideal for homes with less space as they don’t require any additional cold water tanks or hot water cylinders.

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Is a System Boiler Suitable for My Home?

System boilers are best suited to small, medium and large homes with a high demand for heating and hot water.

This is because they can store significant amounts of hot water in the cylinder so two showers or taps can be running at the same time without impacting the water pressure.

However, your home must have enough space to store a hot water cylinder, such as in an airing cupboard or utility room.

Is a Regular Boiler Suitable for My Home?

Regular boilers are best suited to medium and large sized homes with  a high demand for heating and hot water as they can store significant amounts of hot water in the cylinder so two showers or taps can be running at the same time without impacting the water pressure.

However, your home must have plenty of space to store a hot water cylinder, such as in an airing cupboard or utility room and a cold water tank in the loft.

Does iHeat Sell Condensing Boilers?

Yes! We sell and install a wide range of condensing boilers to suit your home. Check out our guide to the best condensing boilers on the market.

Best Boiler Brands: Vaillant, Viessmann, Alpha, Ideal, Worcester Bosch

Selecting the right boiler brand is pivotal for ensuring efficiency, reliability, and longevity in home heating. Among the myriad of options, brands like Vaillant, Viessmann, Alpha, Ideal, and Worcester Bosch distinguish themselves with innovative technology and customer satisfaction. Below is an in-depth comparison of these brands, focusing on their standout models and unique industry positions.

Comparative Analysis of Standout Models


Standout Model

Energy Efficiency

Unique Features

Environmental Impact


ecoTEC Plus


Eco-friendly, quiet operation

Reduced carbon emissions


Vitodens 100-W


Compact design, smart compatibility

Low emissions technology


E-Tec Plus

High efficiency

Compact, cost-effective

Energy-saving operation


Logic Plus


User-friendly, easy installation

Efficient energy use

Worcester Bosch

Greenstar i


Robust build, smart controls

Eco-conscious design


Vaillant's eco-friendly ethos shines in their ecoTEC range, particularly the ecoTEC Plus and ecoTEC Exclusive models. These boast top-tier energy efficiency and reduced carbon footprints. They're known for quiet operation and user-friendly controls, making them a harmonious blend of performance and environmental responsibility.


Viessmann's Vitodens series, especially the 100-W and 200-W, are hallmarks of high-efficiency and technology. These models feature compact designs and stainless steel Inox-Radial heat exchangers for durability. Advanced features like smart thermostat compatibility offer enhanced control and user convenience.


Alpha Heating Innovation's E-Tec range, particularly the E-Tec Plus, offers a fine balance between affordability and quality. Notable for their impressive energy efficiency and compact size, these boilers are suitable for various home types, making them an ideal choice for straightforward, efficient heating solutions.


Ideal Boilers, especially the Logic Plus range, are lauded for their reliability and value. These boilers stand out with their efficiency, user-friendly interface, and compactness, favoured for their ease of installation and maintenance. They come with comprehensive warranties, offering peace of mind and reliability.

Worcester Bosch

A leader in the market, Worcester Bosch is synonymous with quality and reliability. The Greenstar range, including models like Greenstar i, Si, and CDi, is known for its efficiency and robust build quality. These boilers blend innovative features such as smart thermostat compatibility with user-friendly controls, making them a top choice in many homes.

New Boiler Costs

Boilers can be a daunting purchase for many people as they’re an appliance with a lot of responsibility, providing heat for you and your family is something you want to get right. Boilers aren’t exactly a quickly disposable item either, potentially lasting you a decade.

Boiler costs can be split into two segments: the first is the actual boiler itself (unit price), and the second is the cost of the boiler being installed (set up) in your property by an expert engineer. 

Here at iHeat, we want to remove all of this undue stress and make the decision making process of upgrading to a new central heating system, as easy as possible.

Boiler costs can vary depending on a number of factors including their brand, model, fuel, output, warranty, labour and installation type. Typically a new boiler will cost between £1,845 and £3,500, below is a list of average boiler installations offered by iHeat (guide only).

Installation Type

Price (inc VAT)

Combi to combi swap


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System to combi conversion


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New boiler install


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Back boiler to a combi


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System to system


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Frequently Asked Questions

What are the main differences between condensing and combi boilers?

Condensing boilers are designed to increase energy efficiency by extracting and utilising heat from hot flue gases. This reduces heat loss and improves boiler efficiency. A combi boiler, on the other hand, is a type of boiler that coordinates both central heating and hot water in one unit. This means hot water is supplied on demand without needing a separate cylinder. It is worth noting that modern combi boilers are also condensing boilers, which means they take advantage of this increased energy efficiency.

Which boiler type is more energy efficient?

Condensing boilers are generally more energy efficient due to their design. Both combi and condensing boilers offer energy-saving benefits, but a condensing combi boiler would be the most efficient choice combining the advantages of both systems. These boilers can achieve efficiency ratings of over 90%, reducing energy consumption and lowering energy bills.

What are the pros and cons of condensing boilers?

Pros of condensing boilers include:

  • High energy efficiency, resulting in lower energy bills
  • Reduced carbon footprint
  • Better heat transfer rates
  • Compact and space-saving design

Cons of condensing boilers include:

  • Higher upfront cost compared to non-condensing boilers
  • Potential for plume (visible steam) in the exhaust, which may need planning permission
  • Additional maintenance requirements for the condensate drainage system

Do condensing boilers require a water tank?

Condensing boilers do not necessarily require a water tank. If it is a combi-condensing boiler, a water tank is unnecessary, as the boiler will provide hot water on demand. However, a system or regular condensing boiler will typically work in tandem with a hot water cylinder, which stores hot water for the property.

What factors influence boiler prices in the UK?

Several factors impact the price of a boiler:

  • Boiler brand: Renowned brands may have higher price tags
  • Boiler type: Combi, system, and conventional boilers have varying costs
  • Boiler power output: More powerful boilers tend to be more expensive
  • Installation costs: Charges for installation services vary depending on location and complexity
  • Energy efficiency rating: Higher-rated boilers are generally pricier, but lead to long-term savings

How do I know if I have a condensing boiler?

Identifying a condensing boiler can be done by checking the vent pipe leading out of the boiler. Condensing boilers contain a white plastic pipe, whereas non-condensing models often have a metal one. Another clue comes from the energy efficiency rating on the boiler's label; a rating of ‘A’ usually indicates a condensing boiler. If in doubt, consult the manufacturer or an expert heating engineer.

Stephen Day profile photo
Article by
Stephen Day | Co-founder
Gas Safe registered and FGAS certified engineer with over 20 years experience in the heating and cooling industry.