Most Energy Efficient Boilers in the UK (2025)

Swapping out an old, inefficient boiler for a brand-new, highly efficient one can make a huge difference. This can result in lower energy bills and reduce carbon emissions, meaning your home will be warmer and your water will be hotter.

But what is the most energy efficient boiler in the UK? We compared multiple boilers with the highest energy efficiency rating and lowest energy wastage and gathered them to make this guide. Our list includes the most efficient combi boilers, system boilers, and conventional boilers from the best boiler manufacturers on the market. We’ve also included typical new boiler costs and their prominent energy efficiency features. 

If you’re ready to save money on energy costs by upgrading your boiler, why not contact us today for free professional advice? Using our simple 30-second form, you can get up to 3 no-obligation quotes for your new boiler installation. 

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To gather our most efficient boiler list, we carefully studied the market proposition, boiler reviews in the UK as well as global industry trends. Here are the criteria we used in our research:

A combi boiler is a type of heating system that provides both hot water and central heating from a single unit, making it a space-saving choice. All new boilers also use condensing technology, which means that any heat that would be wasted during use is recycled back into the system, making them more efficient than ever before. 

Below are three of the most efficient gas combi boilers available on the market right now.

This compact boiler from Viessmann comes with a standard energy efficiency rating of up to 98%, so you are guaranteed energy savings from this boiler. 

It’s best suited for small to medium-sized homes with fewer than 2 bathrooms. However, this model is available in outputs from 3.2 to 32kW giving you a more accurate power range to choose from. 

This smart set-up also includes durable stainless steel parts, simple operation and a sleek design. It can also be used with WiFi for optimal control and convenience. 

Worcester Bosch boilers are renowned for being reliable, high-quality models which come with an impressive efficiency rating of 94%. This boiler is praised by homeowners for being customer-friendly and worth the investment. However, other customers mention that this boiler exceeds hot water requirements for their small home. 

This stylish gas combi boiler is compact (440x780x365), easy to install and rated as one of the quietest boilers available (53dB). Worcester Bosch also offers an extended 10-12 year warranty, which means you can let this boiler work hard for you without worrying about performance (terms apply). 

This range of Vaillant boilers has recently been remastered to provide users with even more great features. This combi boiler boasts an impressive 94% efficiency and adjusts to preferred heat output through its 1:10 modulation feature. This means that this model can reduce its maximum output to just 10% of its full capacity vs 20% for boilers with a 1:5 modulation ratio.  

Using the vSMART app, as well as the ability to connect to Apple and Amazon devices, this boiler can integrate with smart thermostats like Nest and Hive. With more control, you can save even more on fuel consumption and reduce carbon emissions. 

They have even included more hard-wearing tech inside, with ‘IoniDetect’ to further reduce fuel consumption and increase overall lifespan. 

Can't choose the most efficient combi boiler that will fit your home perfectly? Then we recommend requesting quotes from multiple installers to get the most tailored advice. This means you can compare prices and avoid paying more than you need to. 

To avoid the hassle of endless hours spent internet scrolling for deals, let us bring the quotes to you! Our completely free, 30-second form can connect you with up to 3 local boiler installers in no time. They can provide you with free, no-obligation quotes for you to compare.

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Conventional boilers, also known as ‘regular’, ‘traditional’ or ‘heat only’ boilers, are mostly found in older homes. They consist of three separate elements, a boiler unit, a hot water cylinder, and a cold water tank (which is usually located in the loft). 

Due to the many aspects involved, it's best if conventional boilers are being installed as a direct replacement. As they need a lot of pipework, and installation can take time, it can end up costing you more to choose this option.

We’ve listed 3 of the best energy-efficient conventional boiler upgrades below.

The Greenstar 8000+ regular boiler reaches 94% seasonal efficiency. This boiler has a range of smart features and wireless connectivity options for precise temperature management and optimised energy usage. It is compatible with smart thermostats like Bosch EasyControl, Hive, and Nest for remote control and monitoring.

Homeowners praise this boiler for its reliance and efficiency, highlighting noticeable savings on energy bills and reduced gas consumption. There is also an option to get a 12-year guarantee when installed by a Worcester Bosch Accredited installer.

This regular boiler offers a 93% efficiency for any home that wants to upgrade its conventional heating system.  

With a range of power outputs and a compact build, there is sure to be a model to suit your home's size and demands. It is also suitable for fully pumped open vent and sealed systems and compatible with Baxi’s Megaflo Eco Cylinder.

This model is also noted for its extremely quiet operation and NOx class 5 emissions rating (with 6 being the highest), signifying its low environmental impact. 

Ariston's Clas ONE R is a conventional gas condensing boiler with a 94% efficiency which at the same time won't break the bank. This Ariston boiler has a 40% larger stainless steel heat exchanger (compared to its previous models), which allows for improved hydraulic performance and reduced risk of blockages. 

Its Auto function technology prevents excessive flow temperature peaks by monitoring and adjusting the heating system's temperature, improving the boiler's performance and efficiency.

It's fair to notice that this boiler isn't hydrogen-ready or solar-compatible. What makes it a highly energy efficient gas boiler is its anti-frost system which prevents excessive energy usage by protecting the boiler from freezing temperatures.

Are you tired of soaring energy prices or unreliable heating? Why not give your home the treatment it deserves with a brand-new boiler upgrade?

Whether you’re looking for an energy-efficient replacement for your conventional boiler, or a high-efficiency gas boiler to replace an old boiler that keeps breaking down, we’re here to help! 

Don’t waste time trawling the internet, hunting for trustworthy installers and reading hundreds of reviews, only to wait months for big companies to respond to your enquiries. 

Instead, fill out our quick (30 second) and easy form and in just a few clicks, we’ll find you up to 3 free quotes!  Using our trusted network of certified engineers, we can find you the very best prices from installers in your local area. Then you can compare them to pick one that suits your budget. 

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For homes with a high demand for hot water, such as those with multiple bathrooms, you are most likely to need a system boiler. These boilers work alongside a hot water storage cylinder to ensure your home has an ample supply of hot water on demand. 

Below are 3 of the most efficient gas system boilers you will find today.

The 200-W system gas boiler is one of Viessmann's top products, offering up to 98% energy efficiency. It is designed to meet the heating requirements of both single-household and duplex buildings and offers an impressive 1:13 modulation ratio for even lower heating output.

It comes with condensing boiler efficiency, a stainless steel heat exchanger, and solar thermal integration, which offers efficient heat transfer and supports renewable energy options. 

Viessmann also offers an extended 12-year warranty, giving you further peace of mind (terms apply). 

Ideal Heating has been in the business of boiler production for over 100 years! Their innovative heating technology has enabled them to offer this Logic Max System²  boiler with an efficiency of up to 94%. 

It’s also a lightweight model with a compact design (700mm x 395mm x 278mm), which allows for kitchen cupboard installation. It has been awarded a ‘Quiet Mark’, producing just 36dB of noise, which is comparable to the sound of a whisper or soft music. 

Fitted with hard-wearing parts, a large digital display and smart capabilities, this system boiler is the perfect unit to help you make savings. 

ATAG is one of the less well-known boiler manufacturers on the UK market, but it consistently delivers reliable and efficient heating systems, scoring a 4.8 Trustpilot rating. Homeowners praise its quiet operation, cost-efficiency, and remote control capabilities.

This system boiler option features a lifetime stainless steel heat exchanger, which prevents corrosion and extends the boiler's lifespan. Its weather compensation feature analyses external conditions and adjusts system flow temperatures to reduce energy waste.

ATAG iS suits homes with limited installation space as it can fit inside kitchen cupboards. This model is also compatible with ATAG ONE and Tado V3+ controllers for remote monitoring and control. 

Opting for the most efficient boiler, you could save £490 every year on energy bills. By burning less gas, you will also be reducing your carbon footprint and contributing to better environmental quality. 

But with so many options available, finding the most energy efficient boiler that would fit your needs and budget might become an overwhelming task. 

So that high upfront costs don't scare you away, applying for different boiler grants can help you replace your inefficient boiler for free, or for a reduced cost. So not only could you save on a new installation, but you will be saving money long-term on reduced bills as well. 

When replacing an old boiler, we recommend finding and comparing quotes from multiple installers. This way you get the best professional advice and choose the price that suits you. 

However, we know searching for prices can be stressful and take up hours of your precious spare time.

Let us do all the hard work for you! Our 30-second form finds you quotes in just a few clicks. Within 48 hours, up to 3 certified installers will get back to you ready to discuss the most efficient boiler in the UK for your home.

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