Energy efficient combi boilers

Energy efficient combi boilers, along with other energy efficiency improvement measures, can shave 40% off of your annual energy bills.

Don’t take our word for it.  That’s according to the UK’s Energy Saving Trust.

Here, we’ll give you the best, most factual information on how energy efficient combi boilers can help you save money, and an unbiased review of which brands have the most energy efficient combi boilers in the UK in 2021.

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But first let’s take a look at some DIY (do-it-yourself) techniques, so you spend the least of your hard-earned money on heating your home.

Ways to Improve Energy Efficiency of Your Home

Cheaper Short-Term DIY Options (Small Impact):

  • Draught-Proof and Insulate your Doors/Windows
  • Switch to a Cheaper Energy Provider
  • Buy Energy-Efficient Electrical Appliances
  • Switch to a Programmable Thermostat
  • Consider a Smart, Internet Enabled Learning Thermostat like Nest
  • Hang Thick Curtains

More Expensive Long-Term Options (Big Impact):

  • Switch to a New Condensing Boiler
  • Cavity Wall Insulation
  • Insulate your Attic/Loft
  • Double Glazed Windows
  • Consider Solar Panels

One of the most important options listed above is switching to energy-efficient combi boilers, which we’ll go into more detail below.  But how does cavity wall insulation help?  35% of heat loss from your average house is through external walls.  Studies over the years suggest that every square metre of cavity wall insulation will save more than a tonne of carbon dioxide over the average life of the building.  That’s crucial not just for your wallet, but also for the overall health of the planet that we will leave behind for future generations.

Let’s look at how condensing boilers can help.

Benefits of a New Condensing Boiler

According to the Energy Saving Trust, “If everyone in the UK with Mains Gas, LPG or Oil central heating installed a high-efficiency condensing boiler with full sets of heating controls, we would save enough energy to heat nearly 1.9 million homes for a whole year and save around 6.7 million tonnes of CO2.”

We’ve published detailed, factual posts on our blog previously explaining how a condensing boiler works and answered frequently asked questions like “Condensing or Combi Boiler?”

How do Condensing Boilers Work?

If your existing boiler is more than 12-15 years old, it is not a condensing boiler.

An older, non-condensing boiler wastes heat in the form of hot gases that escape into the atmosphere via a flue out of your house.  If it’s a horizontal flue, it goes out through a back or side wall.  If it’s a vertical flue, the hot gasses escape through the chimney or roof.

A condensing boiler recycles those hot gasses through the primary heat exchanger and uses it to reheat the returning water from your radiators.  This means the burner won’t have to work as hard, saving you money by saving energy.

The diagram below explains it in more detail:

energy efficient combi boilers

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How can Energy Efficient Combi Boilers Save You Money?

As technology evolves, the focus has largely been on making more energy-efficient devices that consume less energy.

With an older, non-condensing, low-efficiency boiler that keeps breaking down, you’re not only wasting your hard-earned money on repairs.  But also wasting more fuel than needed to heat up your house.  So, you’re haemorrhaging money needlessly without even realizing it.

Energy efficiency means using less fuel to give the same, if not better results.  Older non-condensing boilers started off at 85% energy efficiency and over the years due to corrosion and thermal & mechanical stresses, dropped down to 70% or even 50% efficiency.

How does Energy Efficiency Translate into Money?

If your older, non-condensing boiler started at 85% efficiency, that meant every £100 that you spent on energy, you started off losing £15.  Which over the years grew to £30 (at 70% efficiency), and £50 (at 50% efficiency) lost simply due to a boiler operating at low efficiency.

New condensing boilers start off at 90% energy efficiency, and can climb up to 92% to 94% efficiency with the help of programmable thermostats or smart, internet-enabled thermostats and weather compensation.  That’s only £8 or £6 lost on every £100 spent on energy.  Which is minimal.

Then you have high end, top of the line, premium condensing boilers like the Viessmann Vitodens 200-W that go up to a jaw-dropping 98% efficiency.  Even 100% in some cases by recycling outside air and by always being in condensing mode.  The money lost there is £2, or none at all!

That can easily translate into savings of more than £500 per year on your energy bills!  Over 5 years that is £2,500 saved, and over 10 years it amounts to £5,000.  That’s enough money to buy a car or afford a vacation.  Furthermore, because it’s a new boiler, you get 10 years warranty which combines excellent technical support and backup with a service engineer at your beck and call in case of any boiler issues.

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Most Energy Efficient Combi Boilers UK 2021

PLEASE NOTE: All combi boilers manufactured in the last 12 years are condensing boilers.

A lot of people get confused about this.  All combi boilers available today are condensing boilers.  In fact, all boilers manufactured today, whichever brand, are condensing boilers.

Let’s look at the best energy efficient combi boilers money can buy in 2020.

1. Viessmann Vitodens 200-W Combi

most efficient combi boilers, viessmann vitodens 200-w

Energy Efficiency: 98%

Approx. Price (Boiler Only): £1,400 inc. VAT

Approx. Price (Boiler + Installation): £3,000 inc. VAT

This is one of THE most energy efficient combi boilers money can buy in the UK at the moment.  It’s one of the most powerful residential boilers available, because it’s almost as powerful as a commercial boiler.

Viessmann were primarily a commercial heating manufacturer, with many of the world’s biggest stadiums, corporate buildings, malls, even some royal palaces etc. kept warm by Viessmann’s central heating solutions.  A little known fact, Vaillant’s manufacturing plant in Germany has a Viessmann commercial boiler because Vaillant couldn’t find or build one big enough!

So, not so long ago, Viessmann decided to test waters in the domestic boiler market.  And ended up making some of the most reliable, durable and highest energy efficiency domestic boilers in Europe and North America.

As we mentioned earlier, this boiler operates at an amazing 98% energy efficiency with a combination of high quality internal components, innovative engineering solutions, and Viessmann’s Weather Compensation.

Key features of the Vitodens 200-W:

  • Up to 98% of the fuel used is converted into heat
  • At only 34db, one of the quietest boilers available in the UK
  • High Quality Stainless Steel Inox-Radial Heat Exchanger
  • Easy to operate Vitotronic control unit with 5 inch colour touchscreen
  • Control via app and internet (with optional Vitoconnect 100 WLAN adaptor)
  • Environmentally responsible MatriX cylinder burner
  • Lambda Pro Combustion Controller Automatically Adjusts to Different Gas Types
  • No LPG Conversion Kit Required
  • Compact dimensions, only 450 mm wide
  • Energy efficiency class: A
  • Also available as a system boiler (type B2HB)
  • System boiler: Cascade with up to six boilers to 594 kW possible
  • Optional remote fault notifications for Viessmann Trained Installers
Interested in the Viessmann Vitodens 200-W Combi?

2. ATAG iC Economiser Plus 35 Combi

most efficient combi boilers, ATAG

Energy Efficiency: 94%

Approx. Price (Boiler + Installation): £2,600 inc. VAT

ATAG are a manufacturer from the Netherlands, and with their unique stainless steel heat exchanger, are a surprise at number 2 in this list.  Their primary heat exchanger condenses twice, which is why they can achieve a high energy efficiency figure of 94% and above.  And that makes them one of the most energy efficient combi boilers available in the UK at this moment.

Key features of the ATAG iC Economiser Plus 35:

  • Compact Dimensions
  • 10 year warranty
  • Instant hot water with pre-heat facility
  • Built in Passive Flue Gas Heat Recovery Device
  • Comes with an outside weather compensator as standard
  • Achieves ErP ‘A’ rating for heating and hot water
Interested in the ATAG iC Economiser Plus 35 Combi?

3. Viessmann Vitodens 100-W Combi

most efficient combi boilers, viessmann vitodens 100-w Boilerhut

Energy Efficiency: 92% to 94%

Approx. Price (Boiler Only): £1,200 inc. VAT

Approx. Price (Boiler + Installation): £2,600 inc. VAT

This is one of Viessmann’s highest selling boilers in the UK and rest of Europe.  It’s a solid, high efficiency mid-level boiler that sits between the entry level Vitodens 050-W and the high end Vitodens 200-W (number 1 in this list).

For our in-depth, factual review of the 100-W, please click the following link: Viessmann Vitodens 100-W Review

Key features of the Viessmann Vitodens 100-W Combi:

  • Compact design and low weight
  • Quiet operation thanks to low fan speed
  • Available in outputs from 4.7 to 35 kW
  • High quality stainless steel Inox-Radial heat exchanger
  • Class A rated for energy efficiency
  • Low CO2 emissions for reduced environmental impact
  • User friendly Backlit LCD Touch screen for easy operation
  • Optional room thermostats available
  • Up to 10 year extended warranty available if installed by Boilerhut

Interested in the Viessmann Vitodens 100-W Combi?

4. Vaillant ecoTEC exclusive with Green iQ combi

most efficient combi boilers, vaillant ecotec plus with green iq combi Boilerhut

Energy Efficiency: 90% to 92%

Approx. Price (Boiler Only): £1,400 inc. VAT

Approx. Price (Boiler + Installation): £3,000 inc. VAT

One of the reasons why Vaillant don’t score higher than Viessmann is because they still choose to use aluminium for their heat exchangers for most of their boiler models.  They do use stainless steel for some of their boilers.  This boiler from Vaillant has its merits.  It’s one of the most energy efficient combi boilers in the UK, and Vaillant’s lowest fuel consumption boiler model.  Vaillant also claim 85% of its parts are recyclable at the end of its life.  This boiler can be programmed and controlled from your smartphone or tablet as well.

Key features of the Vaillant ecoTEC Exclusive Combi:

  • Quiet operation
  • Flow rate of 17.8 litres per min for fast instant hot water
  • ErP A rated for both hot water and heating efficiency
  • Dimensions in mm (43kW): W 720 x H 440 x D 474
  • Works with LPG where required
Interested in the Vaillant ecoTEC exclusive with Green iQ combi?

5. Viessmann Vitodens 050-W

most efficient combi boilers, viessmann vitodens 050-w Boilerhut

Energy Efficiency: 89% to 90%

Approx. Price (Boiler Only): £900 inc. VAT

Approx. Price (Boiler + Installation): £2,200 inc. VAT

For a detailed breakdown of why the Viessmann Vitodens 050-W is a fantastic choice of boiler, watch the video review below:

The 050-W is Viessmann’s entry level model, but still one of the most energy efficient combi boilers available in the UK.  It has surprisingly good performance at an incredibly affordable price.  What’s more, Viessmann have been consistent with using the inox-radial stainless steel heat exchanger throughout their boiler range.  And that stands for the 050-W as well, even at this price.  And it’s also compatible with weather compensation.  It starts off at around 89% efficiency, with programmable thermostats and weather compensation, it can go up to 92% and 94% efficiency.  Again, mighty impressive for its price.

Key features of the Viessmann Vitodens 050-W Combi:

  • Ultra Compact – Just 707mm in height
  • DHW output ratings of 5.9 to 35 kW
  • High Quality Stainless Steel Inox-Radial Heat Exchanger
  • Integral instantaneous water heater
  • High efficiency – up to 97% (Hs) [gross cv]
  • Low CO2 emissions for reduced environmental impact
  • Digital user interface with LCD display for easy operation
  • Optional room thermostats, plug in time clock and wireless receiver 
  • Up to 7 year extended warranty available
  • Class A rated for energy efficiency
Interested in the Viessmann Vitodens 050-W

6. Worcester Bosch Greenstar CDi Compact

most efficient combi boilers, worcester bosch greenstar cdi classic Boilerhut

Energy Efficiency: 94%

Approx. Price (Boiler Only): £1,200 inc. VAT

Approx. Price (Boiler + Installation): £2,178 inc. VAT

Worcester Bosch make reliable, energy efficient combi boilers.  And have enjoyed being the UK market leader for boilers for many years.

However, are they resting on their laurels a bit too much?

Worcester Bosch’s best model, while comparable to the Viessmann 050-W and 100-W in terms of energy efficiency initially, drops down in ranking due to Worcester Bosch’s decision to stick to aluminium for their heat exchangers.  When we look at energy efficient combi boilers, we also look at other factors like durability and reliability.  And whether the boiler is energy efficient for a long time.

Aluminium is below par compared to stainless steel, no matter which way you look at it.  So, Worcester Bosch boilers will be great for the first 5-6 years or so and then drop down massively in efficiency.  Check out this heat exchanger comparison graph below:

energy efficient combi boilers, heat exchanger comparison

As you can see, the performance drops down dramatically after the first 1000 to 1500 operating hours of a boiler with an aluminium heat exchanger.  We’ve had Worcester Bosch customers call us after the first 6 years of their boiler’s life, wanting to change.

Having said all that, we can’t be too critical of Worcester Bosch.  They do manufacture high efficiency boilers, and as a brand take care of their customers well.  But the fact is you will save more money on energy bills, for longer, with better offerings from other brands.

Key features of the Worcester Bosch Greenstar CDi Compact:

  • Low energy pump reduces electrical usage
  • Frost protection is included, reducing frost risk if installed in a garage or a loft
  • Larger two bathroom properties can be supplied by higher output options
  • Wide choice of controls enables greater comfort and economy
  • Instantaneous hot water, always available
  • Inbuilt keyless filling link making it easy to refill your system
  • Large Condensesure style siphon built into the boiler – eliminates frost risk
Interested in the Worcester Bosch Greenstar CDi Compact?

Energy Efficient Combi Boilers Installed by Boilerhut

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