Most Efficient Boilers: Combi, Gas, & More (2024)

Energy efficiency is a crucial part of picking out a boiler. Higher boiler efficiency can decrease your energy consumption, save on bills, and ensure sustainable operations. While most boilers in the UK are above 90% (on paper), the efficiency of boilers can vary depending on their model, type of boiler, fuel type, and more.

In this article, we’ll look at how efficiency ratings work, the types of boiler efficiency ratings in the UK, and show our candidates for the most efficient boiler in multiple categories.

However, if you’re looking for an energy-efficient boiler, you will need the help of a professional installer. With a reliable installer you can save on new boiler cost and installation, but finding one can be quite a hassle that can take days of research if undertaken on your own.

Instead, our service can easily provide you with up to 3 free, non-binding quotes from reliable installers we’ve vetted ourselves. All you have to do is fill out a quick, 30-second form and we’ll handle the rest. Click the button below to get started.

Boiler efficiency denotes the percentage of how much energy is used for heating compared to how much is wasted during operation. The higher the efficiency, the less energy is wasted while the boiler operates.

Many factors affect the efficiency of your boiler, including its age, the type of boiler, the fuel type, and the specific model. Most modern boilers are above 90% but over time they can lose efficiency. Similarly, certain condensing boilers have much better efficiency than non-condensing ones.

Efficiency is measured in percentages, often categorised into ErP ratings ranging from G to A+++. Boiler efficiency ratings can get tricky when discussing different fuel types.

For example, an electric boiler can be 99% efficient but still be rated lower because it consumes more energy from power plants than a gas model, indirectly giving it a high carbon footprint from the electric grid unless it is hooked up to solar panels or renewable energy systems.

In terms of the type of boiler, efficiency can vary. For larger homes, it can be more efficient to have a boiler that stores hot water, but for smaller homes with lower water demand, this might be excessive. Heating water on demand in the way that combi boilers do can be more efficient for homes with 1 or 2 bathrooms and low water demand.

If you’re wondering, “How efficient is my boiler?” you can find out by checking the ErP label on it. It should be somewhere on the boiler’s exterior. Although SEDBUK boiler efficiency ratings are not as frequently used, they can provide some insight into the details of your heating system, so be sure to look into those as well.

Comparing these measures can shed more light on your boiler’s efficiency since most boilers have an A or B rating under the ErP system. SEDBUK can thus be more useful for boiler efficiency comparisons.

However, keep in mind that the “on paper” boiler energy efficiency is not the same as the actual efficiency, which will always be lower, even for the best boilers. Similarly, gas and electric boilers are judged on different scales since 99% efficient electric boilers can still be less sustainable due to reliance on the fossil-fuel grid (which is why they are categorised as D-rated despite seemingly high percentages). This can make it difficult to compare boiler efficiency.

Still, acquiring an efficient boiler can be a great way to reduce your heating energy consumption. Don't take our word for it, though; Here are some reviews from our satisfied customers:

We surveyed over 5,000 homeowners in 2024 as part of our annual survey. 95% of the respondents were satisfied with their new installations.

Let’s summarise the most efficient gas boilers regardless of the category of boiler. We’re judging the highest efficiency boilers and their ability to fit a range of homes as a product line of boilers.

Both the system and combi versions of this boiler are a winner, with the Greenstar 4000 version being a nice compromise between price and power. This Worcester Bosch boiler line has great quality regardless of size/output.

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The Viessmann gas boilers are a popular choice for a very good reason. With a broad range of sizes and outputs, there’s a suitable Vitodens boiler for virtually every type of home. With a wide price range to suit modest and high budgets, Viessmann has a lot to offer.

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Vaillant boilers are becoming some of the most popular heating options in the UK and it’s easy to see why. The EcoTec line is widely lauded for its great customer reviews and user-friendly smartphone-based controls.

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That said, if you need help deciding what size or type of boiler you need, you should reach out to a professional so they can assess your home personally. This could take days of painstaking research and price comparisons if done by yourself. Luckily, you can let us take the wheel.

Our service can help you obtain up to 3 free, non-binding quotes from thoroughly vetted professionals in your area. Click the button below to get started.

An efficient combi boiler will still require a higher output in kW than other boiler types because combi boilers perform a dual function (water and space heating). The typical combi boiler cost is lower than both system and regular boilers when it comes to installation, but they may not be suitable for your home if it has multiple bathrooms and/or high water demand.

Here are our candidates for the most efficient combi boiler in the UK.

As mentioned above, the Viessmann Vitodens is a diverse line with enduring popularity. The 200-W combi boiler is one of the highlights of the series. It can sport 1 to 2 bathroom households with ease and is worth the comparatively high price.

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Another entry from the Greenstar series. This one gets our vote as a combi due to its ability to stay efficient despite the higher capacity. For a combi, it can manage a higher water demand than most making it better than a lot of low-output combis. It also comes with a higher warranty than much of the competition.

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Hand-built in the UK, these boilers can be a great choice for local buyers, offering both decent prices and high availability of parts. Noted for its quiet operation and small design, it’s a great combi for small homes with limited space.

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If you’re interested in buying an efficient combi boiler, you’ll need an installer you can trust. Check out the best prices by filling out a short, 30-second form and we’ll provide you with up to 3 free, non-binding quotes with the best prices.

For homes with larger water demand and more simultaneous running taps, system boilers can be great. Here are our candidates for the most efficient system boiler models.

With outputs ranging from 15kW to 30kW, there’s a lot of variability between these system boilers. It also boasts easy and full compatibility with the Ideal heating controls and frost protection. Additionally, at 26kg, it’s a fairly lightweight unit that can be great for loft or garage installations.

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Offering 15kW to 40kW boilers, ATAG’s IS range is fit for many different home sizes. It also comes with a fantastic 14-year warranty, making it one of the longest-insured products on this list.

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This may be our choice for the budget system option, but don’t let the price tag fool you. It’s a powerful system with a lot to offer. Baxi boilers get favourable reviews from customers and the compact designs of their technologies are always great for saving space.

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Looking for an efficient system boiler? Fill out a 30-second form to receive 3 free, non-binding quotes from installers in your area. Click the button below to get started.

While conventional boilers have not traditionally been high efficiency boilers, modern models have improved quite a lot. Getting a highly efficient conventional boiler can be important since they are built for high capacity and lower efficiency will lead to higher bills.

As a 30kW regular gas boiler, this model of the Baxi Heat series is powerful yet affordable. Low weight and easy to install due to its multiple flue options, the Baxi 630 is easily mountable in several configurations.

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From the widely recognised Greenstar line, this regular boiler can be great for large homes. With a compact build, it can fit into most cabinets. It’s also compatible with Worcester Greenskies solar panels, allowing for reductions in energy consumption along with higher sustainability.

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Available in 15kW, 20kW, and 25kW outputs, the Alpha E-Tec series comes in a variety of price ranges for houses of different sizes. Despite the affordable price, it is built to endure due to parts such as the stainless steel heat exchanger.

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If you’re looking for an energy efficient boiler in the UK, you’ll still need one thing: a trustworthy installer. A good installer can help you save money on purchase and installation costs. The only problem is that finding a reliable one can take days of research and price comparisons when done all on your own. That’s why our service can be a far more effective alternative.

All you need to do is fill out a 30-second form and we’ll handle the rest. We’ll get you up to 3 free, non-binding quotes from installers in your area that we’ve vetted ourselves. With multiple quotes, you can adequately do your boiler comparison, check prices and pick the best one. They can also help you navigate boiler efficiencies. Click the button below to get started.