When your energy company begins to present you with bills this winter, they will not show up lubed. You're already bent over.... so brace yourself. The most energy efficient boiler just might save you a little pain.
- Most Energy Efficient Combi Boilers
- Most Energy Efficient System Boilers
- Most Energy Efficient Conventional Boilers
- How Much Can You Save With An Efficient Boiler?
- What Is The Most Efficient Type Of Boiler?
- How Efficient Is My Old Boiler? (and who cares? 😅)
- What Is The Most Efficient Size Of Boiler?
- Boiler Efficiency Ratings Explained
- Some Tips To Increase The Efficiency Of Your Boiler
Heating accounts for a significant portion of your energy bills, so it makes sense to install the most efficient boiler available.
The basic heat you need to live is the most profitable and joyful way that energy companies can raid your bank account. Nom Nom. 🤤
In a stroke of genius, they’re now able to guilt trip you into buying hilariously overpriced heat pumps whilst manipulating your tariff to keep you well and truly in the the Matrix.
By law, all new boilers must be at least 92% efficient. It’s a law about as regularly used these days as those against Happy Slapping. This means they convert 92% of their energy into heating, with only 8% wasted. In financial terms, this means that for every £1 spent on your heating, 8p is wasted.
However, some boiler brands exceed this standard, allowing you to save even more on heating costs. Frankly, anything more is so incredibly marginal and even if you bought your boiler in a car park, it will at least be capable of 92%+.
And if you replace an old G-rated boiler with a modern condensing boiler, you could save as much as £385 each year. Choosing the most efficient model ensures you maximise these savings.
In this guide, we'll laboriously explore how much you can really save by upgrading your old boiler and highlight the most efficient models available.
PS We fit new efficient A-rated boilers with gas-safe installation nationwide. Simply answer these questions, get your fixed price and you could get it installed as quick as tomorrow.
Please note: As well as selecting an efficient boiler, it’s also important to be aware of the importance of your boiler’s settings when trying to maximise efficiency, including your boiler’s flow temperature.
Most Energy Efficient Combi Boilers
Combi boilers are the most popular type of boiler in the UK, primarily because they provide both heating and hot water from a single, compact unit. Ideal for most homes, combi boilers are efficient and space-saving solutions.
All modern combi boilers have to be “condensing”. Essentially, condensing boilers are built with a new technology called a Flue Gas Heat Recovery system that recycles heat from the flue gases, ensuring that the majority of the heat produced is put to use. This prevents energy waste and means you are getting more for the same amount of money.
To determine a boiler’s efficiency you can refer to the boiler manufacturer’s manual or materials and the efficiency rating will either be stated as a percentage e.g. 94% and/or a letter that denotes its efficiency rating from G, which is the lowest efficiency, to A+++, which is the highest efficiency.
Some of the most efficient combi boilers currently available in the UK include the following:
#1 Viessmann Vitodens 100-W Combi Boiler
The brand's mid-range combi boiler with a powerful punch.
Everything that makes its little brother Vitodens 050-W the super boiler it is and more. The Viessmann Vitodens 100-W should be any homeowner's go-to combi boiler boasting an industry-leading efficiency rating of 98%.
The 98% efficiency rating puts it well above the 92% standard, so if efficiency is your primary aim, the Vitodens 100-W is the best option.
The image above shows a Viessmann Vitodens 100-W installed by the team here at Heatable. Get a free quote from us here.
A familiar endorsement from ‘Which?’ for its remarkably high-end internal parts, a class A rating for efficiency, back-lit LCD display, low fan speed for quiet operation and low CO2 emissions to help ease your carbon footprint and conscience. This is Viessmann’s, Lebron James.
Upgrades on the 100-W vs the 050-W include a larger LCD display with additional options, a superior Printed circuit board (essentially the brain of the boiler) and additional power output options.
The 100-W is also manufactured and assembled in the German Viessmann factory, while the 050-W is assembled in Turkey.
Ideal for: Those looking for a powerful, mid-range combi boiler.
Prefer video? You can watch our complete Youtube review of the Viessmann Vitodens 100 below:
#2 Worcester Bosch 8000 Style (Replacing the CDi Classic)
The brand's premium combi boiler model.
Worcester's most powerful and connected wall-hung boiler to date, capable of delivering up to 50kW's and has an efficiency of 94%.
It also comes with optional smart technology that will top up the boiler for you when low pressure is detected.
As its name suggests, it is also arguably the best-looking boiler on the market and readily available in black - a boiler industry innovation on par with the introduction of the iPod.
Ideal for: Ideal for: Those looking for a top-of-the-range boiler, with all of the latest and greatest features.
Read our in-depth reviews of some of the most popular models from the brand:
#3 Vaillant ecoTEC Plus Combi Boiler
Ideal for: Ideal for: Those looking for Vaillant's entry-level combi boiler.
A broad range of kW outputs starting from 25kW makes Vaillant’s ecoTEC plus the combi allrounder for almost any small to medium home.
With an excellent efficiency rating at 94%, premium components and the addition of the Quiet Mark award for quiet operation make this Vaillant’s flagship boiler.
Ideal for: Anyone looking to secure themselves Vaillaint's mid-range or so-called 'flagship' combi.
Most Energy Efficient System Boilers
If your home has a high hot water demand e.g. multiple bathrooms that are likely to be used at the same time, you will probably require a system boiler.
This type of boiler works in conjunction with a hot water storage cylinder to ensure your home always has a sufficient supply of hot water at times of peak demand.
Like combi boilers, there are many models that now exceed the standard 92% efficiency rating, including the following:
#1 Viessmann Vitodens 200-W System Boiler
The brand's range-topping boiler model is perfect for larger homes.
Meeting every demand a boiler buyer could possibly have for their system boiler and achieving an industry-leading efficiency rating of 98%
The Vitodens 200-W is perfectly suited for larger detached and semi-detached homes.
It holds every feature and perk of Viessmann boilers before it whilst also boasting a colour touchscreen display, smart thermostat compatibility and up to an incredible 98% efficiency rating.
Ideal for: Those looking for the top-of-the-range combi boiler from the award-winning German brand.
Most Energy Efficient Conventional Boilers
Just like system boilers, conventional boilers, also known as "‘heat only’ and ‘regular boilers’ are more appropriate for homes with more demand for hot water.
Unlike system boilers, they require a cistern in the attic and so can limit the installation locations available to you.
No longer the ideal choice, conventional boilers are still a great option for homes that already have them installed and would like to keep costs low by avoiding a heating system conversion.
Thankfully, there are some efficient conventional boiler models out there and here are some of the most efficient:
#1 Worcester Bosch 8000 Life Conventional Boiler
The Worcester Bosch Greenstar 8000 series is the brand's premium, highly efficient, design-led offering, which includes two standout models: the Greenstar 8000 Life and the Greenstar 8000 Style.
The Worcester Bosch Greenstar 8000 series offers a blend of high performance, efficiency, and modern design, making it a top choice for homeowners looking to upgrade their heating systems.
The key difference between the Life and Style models lies in their design and user interface, allowing consumers to choose based on their aesthetic preferences and control needs.
How Much Can You Save With An Efficient Boiler?
If you replace your old boiler, the amount of money you can save will depend on the rating of your old boiler and your property type.
The table below displays the estimated savings you can expect based on the current energy price cap:
Old Boiler Rating: | Bungalow | Detached House | Flat (Mid-Floor) | Semi-Detached House | Mid Terrace House |
G (<70% efficient) | £345 | £640 | £150 | £385 | £320 |
F (70-74% efficient) | £245 | £460 | £100 | £275 | £225 |
E (74-78% efficient) | £195 | £370 | £80 | £220 | £180 |
D (78-82% efficient) | £150 | £295 | £60 | £170 | £140 |
Table data source: Energy Saving Trust. Last updated: July 2024.
What Is The Most Efficient Type Of Boiler?
Boilers lose heat in the form of hot gasses.
However, modern boilers are condensing. This means that they recover more heat from the fuel gasses.
They then use this heat to heat the water, making the boiler more efficient.
Condensing boilers are 25% more efficient than non-condensing ones. Due to this reason, most newly installed boilers are condensing boilers.
So, if you purchased your boiler post-2007, it is very likely that you already have a condensing boiler.
Have a look at the three most commonly used boilers and decide which one is best suited for you.
Combi Boiler
It does not store heated water and heats water as needed. The boiler is compact and does not have any storage tanks. Ideal for smaller homes.Heat-only Boiler
Also called a regular, traditional, and open vent boiler, the boiler has hot water and cold water storage tanks and takes up a lot of space. The boiler is ideal for large houses that have multiple bathrooms.System Boiler
Similar to the heat-only boiler, it has a hot water tank but misses the cold water storage tank. The boiler can provide water simultaneously in two bathrooms and is ideal for large homes.
Combi boilers do not preheat and store hot water.
The water is heated as needed. So, there is no energy wastage in maintaining the hot water.
Thus, the combi boiler is much more efficient than a regular or system boiler.
Also, combi boilers occupy the least space and are suitable for small apartments.
Boiler Fuel Type
Another factor affecting the boiler's efficiency and cost is the fuel type. Condensing gas boilers are the most cost-efficient.
Gas is the cheapest fuel compared to electricity, oil, coal, and LPG.
You can also switch to a low-carbon heating heat pump that reduces the cost depending on the fuel type and system you are replacing.
Sustainable Energy
With most governments aiming for zero carbon emissions, switching to sustainable energy and sustainable fuels is the most sensible option.
However, they are neither cheap nor easy. However, some low-carbon heating systems can be installed.
Let's take a look at some low-carbon emission options:
Solar water heating
This is the most nature-friendly option. You use sunlight to fulfil your heating requirement. Such heaters are equipped with solar thermal panels that use the sun’s heat to heat water.Ground source heat pumps
A network of pipes runs underground in this system. Natural heat is used to heat the water and make it available for the heating system.Air source heat pumps
They work similarly to ground heat pumps but extract heat from the air, not from the ground. They require an additional compressor to increase the temperature.Electric central heating
They run on electricity and reduce carbon emissions; however, they are very expensive.
How Efficient Is My Old Boiler? (and who cares? 😅)
The efficiency of boilers reduces with age and use.
As the boiler ages, the parts may get rusted and the system may get blocked with debris and sludge.
Over some time, the boilers develop a need for regular repair and servicing to ensure efficient working.
Most boilers give an 80% efficiency up to 15 to 20 years of installation.
However, their efficiency will drop to 60% or less once they have aged 25 years. This will take its toll on the fuel bills.
Check out the below table to determine the efficiency of your boiler with respect to its age:
Boiler age (in years) | Efficiency rating | Efficiency percentage |
0+ | A | 90+ |
10+ | B/C | 85+ |
15 | C/D | 80+ |
20+ | E/F | 70+ |
25+ | G | 60+ |
Energy-efficient boilers may have a considerable upfront cost but are more cost-efficient in the long run as you save on heating bills.
What Is The Most Efficient Size Of Boiler?
The size of the boiler is the next key factor affecting cost efficiency.
Larger boilers will have a greater heat output, which means more energy requirement.
Although you need a greater output for larger homes, a small home can do with boilers that have a low heat output.
A boiler too large for the home will use far more heat than required to heat the space and result in carbon emissions and higher bills.
Learn how you can save money by trading in your old boiler for a new, efficient model in our YouTube video below:
Boiler Efficiency Ratings Explained
Consider the following efficiency ratings to determine the one that is the most efficient and suitable for your needs.
ErP energy rating
Modern boilers are rated for efficiency.
They are rated under the European Energy label ErP (Energy-related products).
The boilers are rated from A+++ to F, with A+++ being the most efficient.
Introduced in 2015, all boilers manufactured after that have an ErP rating.
Combi Boilers
ErP gives two ratings for Combi Boilers. One for space heating and another for water heating. The space heating rating is written under the radiator symbol while the water heating rating is written under the tap symbol. The ratings indicate how energy efficient the boiler is in heating the space and water.Heat-only Boilers
They have a single rating from ErP. They are rated for space heating.
ErP also rates the noise level of boilers. The readings are given in decibels (dB). A high
dB value will correspond to a higher noise level. Along with all this, ErP also states the heating output of the oiler in kW.
Most modern boilers today have a minimum of an “A” ErP rating, as the government has made it mandatory.
So, almost any new boiler you get will be energy efficient.
Related reading:
SEDBUK Efficiency Rating
Another efficiency rating is done by SEDBUK (Seasonal Efficiency of Domestic Boilers in the UK).
The system classifies and compares boilers' efficiency in converting fuel to heat.
Initial SEDBUK ratings were done in letters, but that led to a lot of confusion between SEDBUK and ErP ratings. So, letter ratings were withdrawn.
Today, the rating is done by giving an SAP score. There are two different SAP scores, they are:
SAP Winter Efficiency
It rates the room heating and water heating efficiency of the boiler. The measurement is done in independent laboratories, and modern boilers have very little difference concerning SAP Winter efficiency.SAP Hot Water Efficiency
As the name suggests, the rating determines the boiler's efficiency in producing hot water for the taps. There is a huge difference in the SAP hot water efficiency of most boilers, so you must look for the most efficient ones when making a purchase.
Some Tips To Increase The Efficiency Of Your Boiler
Below are some measures that you can take to ensure smooth and efficient working of your boiler:
Keep the boiler clean.
Keep unwanted air out.
Regularly service your boiler.
Watch out for signs that may indicate working problems in the boiler and fix them as soon as possible.
Maximize hot condensate returns.
Energy-Efficient Boilers Conclusion
Energy-efficient boilers are not just economical, they are easy on the environment as well.
They save a lot of money and have negligible carbon emissions.
As the boiler ages, its efficiency decreases, requiring more energy to do the same amount of work.
This increases the fuel consumption and thus your energy bill.
Get your boiler regularly serviced so it is not strained, and even replace it if necessary.
Get a Quote For An Efficient Boiler Today
If you’re aiming to get the best deal on a new boiler, consider getting a quote from us, here’s why:
Gas Safe installation within 24 hours.
Thousands of satisfied customers with an average score of 4.9 on Trustpilot, surpassing the market leader.
Which? Trusted Trader: Heatable is proudly recognised as a Which? Trusted Trader.
Price match guarantee: We will match any like-for-like cheaper quote.
Flexible payment options, including interest-free finance.
Up to 12-year guarantee on selected boilers.
Fixed price guarantee: No hidden costs.
Save your quote and decide later.
Get an instant fixed price on a new boiler, here.
To learn more about boilers, visit our advice section, check out our YouTube channel, or read customer testimonials here.
