Condensing Boilers: The Cost, Efficiency & How They Work

Condensing boilers are a great option for home heating but they do have their drawbacks. Find out more in our guide.

Condensing boilers are light years ahead of older boiler types, meaning the get more heat from less fuel. When upgrading your heating controls and replacing a non-condensing gas G-rated boiler, you could save up to £380 per year. But does it make sense for your home?

What’s In This Guide to Condensing Boilers?

Head straight to the section you need by clicking the links below.

If you are aware of the world’s environmental problems and want to save some money whilst doing your bit, an oil or gas condensing boiler might be right. Due to advances in engineering, these modern boilers are able to use heat more economically.

Most modern oil and gas boilers are condensing and unlike the older non-condensing type, they operate at 99% efficiency using multiple heat exchangers to squeeze all the heat possible out of the fuel.


Condensing Boiler Types

A modern condensing boiler comes in two different types: the system boiler and a combi-boiler. If you have a water tank to store hot water, you can easily combine it with a system boiler. System boilers are an efficient and beneficial solution for large households that have two or more bathrooms and a high volume of water consumption.

How A Condensing Boiler Works

The main principle of a condensing boiler, is that the vapourised steam condenses into heat instead of going through the flue and being wasted. After that, the steam passes through a heat exchanger which cools it off and condenses it back to a liquid form. The heat warms up the water that is pumped from the mains.

Among all the types of boilers available on the market, the condensing boiler is the most effective and energy efficient. Due to the advanced combustion technologies, condensing boilers reduce the level of nitrogen oxide and carbon monoxide thrown out into the atmosphere.

Condensing Boiler: Prices

The average price for condensing boilers, excluding the installation costs, can vary between £1,500-2,500. This is a significant investment, but it will pay off within the period of 10 years. Condensing boilers will help save between 10% and 12% on your energy bill every year.

Whilst the initial cost of a new condensing boiler can be a little high, in the long run, they are a wise investment that will pay off by reducing your energy bills and saving hundreds annually.

The Pros & Cons

Condensing boilers have come along way in recent years and with EU regulations encouraging more efficient central heating systems, the drawbacks to buying a modern gas or oil condensing boiler are minimal.


Condensing Boilers: The Advantages

Condensing boilers are designed to reduce the emissions of greenhouse gases which helps prevent the development of global warming.

By reducing energy waste a modern condensing boiler improves the home energy efficiency and helps reduce your home heating bills.


A condensing boiler heating system is completely sealed and the air that it uses comes from the outside. There are also safety measures installed on a condensing boiler such as heat sensors, which switch the system off if they detect any failure

Condensing Boilers: The Disadvantages

In very rare occasions, the condensation pipe which siphons off acidic waste water, can become frozen due to external weather conditions. This can be easily fixed by pouring warm water over the frozen area.

Do I Need A Condensing Boiler?

Building laws in the United Kingdom made condensing technology mandatory for all new gas boilers in 2005.

They are more environmentally friendly to operate because of their greater efficiency, and they can help you save money on your heating and hot water costs. Furthermore, they are thought to be safer than earlier non-condensing boilers.

According to the Energy Saving Trust, replacing an outdated G-rated non-condensing boiler with a new high-efficiency condensing boiler and updating your heating controls may save you over £300 per year.

Common Condensing Boiler Problems

Modern boilers are quite dependable thanks to all a whole host of technological advancements. However, because each type of boiler is unique, they all have their own set of issues.

A condensing boiler creates a steady flow of condensate, which, just like your sink and washing machine, drains into your household’s waste water or into the sewage system.

If the outlet becomes blocked, your condensing boiler will shut down automatically for safety reasons. A frozen boiler condensate line is the most prevalent cause.

If your boiler has a condensate pipe that is outside the building and thus exposed to lower temperatures, this is the most likely scenario. Although it is a prevalent concern during cold spells, it can readily avoidable and remedied.

What Size Condensing Combi Boiler Do I Need?

When choosing on the size of condensing gas combi boiler to purchase, two important elements to consider are how much hot water you will use and how many rooms you will need to heat. A combi-boiler of 24-30 kW is a reasonable choice for most standard 2-3 bedroom residences with a single bath and shower.

A larger 30-35 kW heater is ideal for homes with an additional en-suite bathroom or more rooms. More guidance and information may be found in our post on selecting the correct boiler for your home.

The Best Condensing Boiler Brands


Since 1866, Baxi has been a leading maker of heating systems in the United Kingdom. Baxi is Endorsed by Which? Trusted Traders for their customer service, installation, and servicing, and employs over 6,000 people in over 100 countries. A terrific new boiler firm based in the United Kingdom.


Vaillant UK is a family-owned business with a history dating back over 140 years. Vaillant Group is the second-largest European heating manufacturer, with a presence in over 20 countries. When it comes to finding the best condensing boilers, ratings are crucial, and Vaillant has a 4.6/5 rating on Trustpilot.


The company was started in 1917 in Germany by Johann Viessmann. It is now a multinational corporation with about 12,300 workers. Viessmann claims to make the most dependable boilers in the UK, and they frequently appear on Which? Best Buy lists. In their home country of Germany, Viessmann was selected the top Energy & Heat brand for 2019.

Worcester Bosch

Originally known as Worcester, they were acquired by the Bosch Group in 1996 after 34 years of operation. Worcester Bosch has two production facilities in the United Kingdom: one in Worcester and another in Derbyshire. YouGov named Worcester Bosch as one of the top recommended brands for home appliances, placing it among the top ten best brands.

Find A Local Installer

Condensing boilers are a modern energy efficient, eco-friendly product, and provide you with multiple benefits. If you consider installing a condensing boiler in your home, it is crucial that the task is performed by experts. In this case, you will need to find a reliable company that can install a condensing boiler safely and will guarantee a high level of quality.

Last Updated on November 6, 2021


Author: Indra Gupta

Indra is an in-house writer with a love of Newcastle United and all things sustainable.

Scroll to Top