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    • Most Energy Efficient Boilers for 2022, 2023 and beyond…

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  • Most Energy Efficient Boilers for 2022, 2023 and beyond…

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    • Blog
    • Most Energy Efficient Boilers for 2022, 2023 and beyond…

    Updated: March 10, 2023

    What are the best energy efficient boilers?

    the most energy efficient boilers are Worcester Bosch, Baxi, Vaillant, Navien and Viessmann. You can find more details about these models on this page.

    Most Efficient Boilers:

    When choosing a new boiler, efficiency is one of the most important factors to look into. It can help you reduce your energy costs as well as your carbon footprint.

    Energy Efficiency Regulations:

    You will save on your energy bills if you have an energy efficient a boiler because you’ll pay less for wasted energy.

    In addition, this increased efficiency will also be responsible for reducing your carbon footprint.

    • All new gas boilers installed in UK are required by law to be condensing boiler, since 1st April 2005
    • Since 1st April 2007, the same law applies to oil boilers as well.

    Boiler efficiency has become more important than before since all boilers available for sale and installation in the UK need to be condensing

    Boiler manufacturers are competing with one another when it comes efficiency, as well as tech and innovation.  They are all trying to utilise innovative and use the latest technologies to increase the efficiency of their appliances in addition to the desirability of their brand.

    Online Boiler Efficiency Guide

    On this page, you will take a look in details at the most efficient boilers available in the UK.

    But before we look at the different efficiency ratings of different boilers we need to understand what Boiler Efficiency refers to.

    What is boiler efficiency?

    The term Boiler efficiency, refers to the percentage of the total energy used by the boiler to provide heating.

    Condensing Boiler Efficiency rating example:

    A 90% efficient boiler will use 90% of the supplied energy for heating your home.

    Lost Energy

    This means that the remaining 10% of energy would have been lost because of the missing 10% of efficiency.

    To clarify, for every £1 you spend on heating your home, only 10p will be wasted.

    It must be said though that a 90% efficient boiler is much more efficient than the older non condensing heat-only boilers which are still being used every day in many UK homes.

    Non Condensing Boilers

    On the other hand, an older non-condensing boiler could be running at an efficiency rating of around 70% efficiency.

    As a result, 30% of the energy you are paying for is being lost and not being used to heat your home. 

    Boiler efficiency ratings:

    Boilers are rated using an energy efficiency rating scheme from A-G, just like other domestic appliances like freezers, washing machines and fridges.

    All new boilers in the UK must be A-rated by law and must conform to Boiler Plus regulations.

    You can see the energy efficiency rating scheme below:

    Efficiency RatingEfficiency (%)
    A90% and above
    Gbelow 70%

    Boiler Plus regulations 

    All new oil and gas boilers must be installed with a thermostat and a programme timer, according to the new UK regulations implement in 2018

    Energy Saving Features:

    In addition all new combi boilers must include at least one energy-saving feature such as:

    A flue gas heat recovery system:

    A system that condensing boilers use to recover heat from exhaust gases.

    A load compensating thermostat:

    A thermostat that adjusts the temperature of the radiators based on the actual room required to heat.

    This thermostat will increase the temperature of your radiators when the room is cold to ensure efficiency.

    It will also decrease the temperature of the radiators when the room is reaching the required temperature.

    A Smart Thermostat:

    A Smart thermostat is an internet compatible system that gives you the ability to control your heating system remotely.

    Remote Control Programming:

    Remote Control Programming enables you to remotely control your heating via a smartphone or tablet.

    In addition smart thermostats can include additional smart functionality like voice control, open window detection & geofencing.

    These are available in hand held devices and via smart phone apps.

    Weather compensation Auto-Feature:

    The automatic Weather compensation feature uses an outside sensor to monitor the outside temperature and regulates your boiler temperature to make sure your home isn’t being unnecessarily heated when it is not required to do so.

    Why are condensing boilers more efficient than non-condensing boilers?

    By getting a new condensing boiler over an older non-condensing boiler, you will be saving money on your energy bills, in addition to lowering your Carbon footprint.

    That’s because condensing boilers work to recover heat that a non-condensing boiler would have lost via the flue.

    This is called a flue gas heat recovery system

    This system works by recovering heat (mostly hot steam with some acidic content) and recycling it, rather than loosing it like the older non-condensing models used to.

    In condensing boilers, the hot flue gases go through a heat exchanger first before exiting through the flue outside. 

    What boiler brand is the most efficient?

    The top 5 most efficient boilers are:

    1. Worcester Bosch Greenstar 24i Gas System Boiler

    • 94% efficiency rating
    • ErP rating: A
    • Condensing: Yes
    • Central Heating Max. Output: 24.6 kW

    As the UK’s leading domestic boiler manufacturer, Worcester Bosch have invested heavily in the efficiency of its boilers.

    The Greenstar 24i is an excellent example of this. Air uses Worcester Bosch’s advanced technologies to achieve a very high efficiency rating of 94%.

    Perfect for medium sized properties

    This boiler is suitable for small to medium-sized homes with up to 15 radiators.

    Greenstar 24i is a system boiler with a very reasonable output of 24kW. 

    The excellent efficiency rating has help the Greenstar 24i to get endorsed by the Energy Saving Trust.

    The WB Greenstar 24i Combi Boiler fantastic features and benefits are:

    • A large & comfortable boiler control plan that is extremely easy to use
    • Lots of user-friendly controls that help users to keep your property at your preferred temperature
    • A highly efficient pump that uses less energy and reduces your electricity consumption 
    • A boiler that works alongside a hot water cylinder to supply the hot water demands for properties with up to two bathrooms
    • Compatibility with the Bosch EasyControl smart thermostat. This allows users to use a smartphone and tablet app for controlling  your heating and hot water remotely.  You can also check your energy usage, and turn off the heating room by room.
    • Compatibility with Worcester-Bosch’s Greenskies solar panels for even further energy efficiencyand cost savings
    • A 7-year guarantee
    • An A-rating for heating and hot water

    2. Baxi 224 Combi Gas Boiler

    • 93% efficiency rating
    • ErP rating: A
    • Condensing: Yes
    • Central Heating Max. Output: 21.8 kW

    Baxi are known for their expertise in manufacturing high-quality boilers that perform well. Thier boilers are very efficient but are sold for a low cost.

    The Baxi 224 Combi Gas Boiler is no exception.

    Championing Baxi’s energy efficiency, the Baxi 224 is also a boiler that’s endorsed by Energy Saving Trust.

    Ideal for smaller homes

    With a maximum central heating output of 21.8 kW, the Baxi 224 is suitable for smaller homes with up to 10 radiators and just the one bathroom.

    The Baxi 224 Combi Boiler fantastic features and benefits are:

    • Baxi 224 is great for properties where space is at a premium due to its very compact size.
    • It has a high efficiency ratingof 93% and a ErP A rating for heating and hot water.
    • The Baxi 224 is highly efficient and is compatible with Baxi’s uSense smart thermostat which complies with Boiler Plus.  When connected using OpenTherm it works to reduce your energy consumption and save you money. With USense you can control your heating remotely via your smartphone or tablet.  This smart technology also learns about your lifestyle and how you use your heating and uses the load compensation as standard.
    • This highly efficient boiler will save you money on your energy bills
    • Up to a 3-year warranty
    • An A-rated boiler for heating and hot water

    3. Vaillant EcoTec Pro 28 kW Combi Boiler

    • 94% efficiency rating
    • ErP rating: A
    • Condensing: Yes
    • Central Heating Max. Output: 24.8 kW

    The EcoTec Pro from Vaillant is a combi boiler suitable for small to medium-sized properties with up to 10 radiators and just the one bathroom.

    Super Smart Technology:

    The Vaillant EcoTec Pro uses super-smart technology which enables it to adapt to your heating demands and only provide you with the heat that you need. As a result, it will help you to lower your fuel bills and thus your carbon footprint.

    Longer Lasting Efficiency:

    The use of a stainless steel heat exchanger which offers reliability and corrosion resistance is key to this boilers energy efficiency.

    The stainless steel heat exchanger will retain efficiency for longer than aluminium alternatives. 

    Further efficiency is achieved by the EcoTec Pro’s integration with Vaillant’s vSMART app:

    The vSMART app enables you to control your heating system using an iOS and an Android app.  It also has a self-learning function.

    This functionality starts to understand your home’s heating needs and makes your boiler work smarter to increase efficiency and minimise your energy bills and carbon footprint.

    In addition to this, vSMART features, this system has a weather compensation feature for monitoring local weather conditions and adjusts your boiler when required to ensure that your home isn’t being heated unnecessarily.

    The EcoTec Pro 28 kW Combi Boiler fantastic features and benefits include:

    • Maximised Energy Efficiency with the use of Innovative Technology.
    • Stainless steel heat exchanger featuring anti-corrosion properties to retain efficiency for a longer time period.
    • Compatibility with a range of wired and wireless controls including Vaillant’s vSMart app for increased efficiency and smart learning about your home’s heating requirements.
    • Auto Weather compensation to automatically regulate the temperature of your home based on outside temperatures.
    • A high-efficiency pump, making the boiler less expensive to run.
    • A boiler that can be easily converted to use LPG.

    4. Navien LCB700 Blue Flame 28 kW Oil Combi Boiler

    • 93% efficiency rating
    • ErP rating: A+ (when used in conjunction with Navien’s Smart Plus control pack)
    • Condensing: Yes
    • Central Heating Max. Output: 28 kW

    Navien is a fairly new to the UK market having only been supplying boilers here since 2014.

    They are a global leader in condensing technology and this shows with the efficiency gains provided by the Navien LCB700 Blue Flame 28 kW Oil Combi Boiler.

    High Efficiency

    Offering an efficiency rating of 93% and an ErP A rating for heating and hot water, the LCB700 utilises Navien’s innovative technology to achieve this high efficiency.

    Key to this efficiency is Navien’s use of a blue flame burner and a stainless steel heat exchanger.

    The Navien LCB700 Blue Flame Oil Combi Boiler fantastic features and benefits are:

    • Navien’s SEDBUK A-rated blue flame burner uses revolutionary technology that replaces yellow flames in oil boilers and guarantees superior efficiency.  It has ultra-low NOx emissions and low pollutant emissions.
    • The stainless steel heat exchanger used in the Navien LCB700 is designed for resistance against corrosion and erosion which will ensure the efficiency of the boiler is retained for a longer period.
    • With a built-in Intelligent Mode, the Navien LCB700’s efficiency is increased by utilising self-learning that monitors your DHW usage and prepares it according to your typical usage routine.  It also continues to monitor usage and will adjust itself accordingly.
    • Further smart functionality and efficiency gains can be achieved by utilising the LCB700 with Navien’s Smart Plus controllers.  These are designed to increase the LCB700’s efficiency and provide you with savings on your energy bills and carbon footprint.
    • A Smart Plus controller will regulate your heating based on changes in outside temperature, utilising geofencing to regulate your heating when you’re not home, enable the boiler to run in condensing mode when operating at maximum efficiency, and allowing you to monitor your oil consumption extremely quickly.
    • Due to its excellent efficiency, the Navien LCB700 Blue Flame Oil Combi Boiler is also endorsed by the Energy Saving Trust.

    In addition to other features and benefits such as:

    • A high/low oil pump system allows continuous optimisation of heat/DHW output
    • Built-in intelligent mode offering self-learning to increase the boiler’s efficiency based on your typical usage
    • An OpenTherm ready boiler allowing for instant access to the latest control technology
    • Compatibility with Navien’s Smart Plus controllers
    • Navien’s industry-leading condensing technology
    • A 10-year warranty

    5. Viessmann Vitodens 100-W 30 kW Combi Boiler

    • 94% efficiency rating
    • ERP rating: A
    • Condensing: Yes
    • Central Heating Max. Output: 25.4 kW

    The Viessmann’s best-selling gas condensing boiler is the Viessmann 100-W.

    This can be attributed to the combination of excellent reliability, efficiency and advanced technology.

    Continued Investment

    Viessmann’s constant investment into product development and continuous improvement has had a great effect in the efficiency of its boiler range. 

    The Viessmann 100-W features and benefits include:

    • Offering a 94% efficiency rating and an ErP rating of A for heating and hot water, the Viessmann 100-W combines high-quality components and advanced technology.
    • The key component utilised by the 100-W is the stainless steel Inox-Radial heat exchanger. Constructed from materials just one grade lower than surgical steel.  This features properties that are self-cleaning and highly resistant to corrosion and erosion ensuring that the boiler will retain its efficiency for longer periods of time.
    • Complemented by Lambda Pro automatic combustion control for maximum efficiency at all times.
    • The 100-W’s MatriX-Plus cylinder burner is environmentally responsible, reducing the boiler’s CO² and NOx emissions, and increasing the boiler’s efficiency.
    • Complemented by Lambda Pro automatic combustion control for maximum efficiency at all times.
    • This efficiency is further enhanced by the Viessmann 100-W’s smart functionality and integrated Wi-Fi, which is a new feature on the 2021 model.

    As well as other features and benefits like:

    • The boiler’s integrated Wi-Fi means that it is compatible with Viessmann’s ViCare app which allows it to be controlled remotely using a smartphone or a tablet without the need for third party controls.
    • In addition to allowing you to control it remotely, the ViCare app will also enable you to increase the boiler’s efficiency of by learning your daily routine and automatically reducing your heating. And in turn, your energy bills. It also allows you to control the heating in specific rooms only in your property, ensuring you aren’t wasting money and energy heating any empty rooms in your property, unnecessarily.
    • Further increasing the Viessmann 100-W’s efficiency is its use of weather compensation technology which will regulate and adjust your heating based on the current weather by utilising an outside temperature sensor.
    • 94% efficiency rating
    • An ErP A rating for heating and hot water
    • An advanced self-cleaning and corrosion and erosion resistant stainless steel Inox-Radial heat exchanger, designed to retain the boiler’s efficiency for far longer than aluminium alternatives 
    • The environmentally responsible MatriX-Plus cylinder burner which extends the boiler’s service life and reduces CO2 and NOx emissions
    • Weather compensation technology to regulate your heating based on the exact temperature outside 
    • 12-year warranty 
    • Many boiler manufacturers such as Worcester-Bosch, Baxi and Ideal use an aluminium heat exchanger manufactured by a third party based in France
    • Stainless steel is a more efficient and corrosion-resistant metal compared to aluminium and will last longer.

    So Why Let’s Heat!

    We fit 4 different types of boilers and heating systems!

    We supply and install the following 4 different types of boilers and heating systems:

    1. The Common, Heat Only Boiler
    2. A System Boiler
    3. Combi Boiler
    4. The new Heat Pump!

    If you need more info on any of these other boilers or pumps please click the links.

    Finance for your boiler…

    Buying a new boiler and having a boiler installation or a heat pump, is an investment.

    However it can be expensive, especially paying for it all in one hit.

    FCA Approved

    If you haven’t got the money on hand for the boiler and installation services that you require, you can get the job done on a finance package that is FCA-approved.

    We can also offer a number of split payment options for you to consider.

    Boiler Replacement Payment Options

    For new boiler installation, you can pay by card, pay zero deposit, and pay monthly over 2 to 10-years or take our a finance package.

    So why Let’s Heat for your combi boiler replacement?

    A. Let’s Heat Are Quality & Accredited Boiler Installers

    Let’s Heat professional engineers and emergency plumbers provide a professional and reliable emergency plumbing and heating service.

    Our Coverage

    Our service includes solutions like; Boiler Installation, Heat Pump Installation, Pump & Boiler Repair & System Maintenance.

    Thieve services are provided to homes and businesses in Cardiff and the surrounding CF postcode areas of South Wales.

    We also cover the rest of Wales and all of England (see below).

    High Standards – 365 & 24/7

    The installation & repair team are all fully qualified to the highest standards and take pride in producing exemplary work standards.

    This includes completing all boiler installation requirements no matter what time or day this is required!

    Qualifications & Accreditations:

    Our team of high-quality professional engineers has an extremely high 4.9 out of 5, Trustpilot score given by our previous happy customers.

    We are fully accredited by Gas Safe and Corgi registered, as well as FCA approved for all of our financial transactions.


    All of our staff at Let’s Heat are experts in their field and have gathered many years of experience.

    This has been obtained whilst working on a wide selection and variety of emergency plumbing and heating solutions and services throughout Cardiff, Wales & the UK.

    B. Because we care…

    Are you still a little confused about where to start or who to use?

    Our easy-to-use online questionnaire will guide you through everything that you, and we, need to know. This will ensure that you have the correct solution for your needs.

    We will also ensure that you are completely satisfied with the solution offered prior to completing any works.

    Why else?

    Because of additional benefits like;

    • Coverage of all of England & Wales.
    • Reliable, professional, and trustworthy.
    • High Trustpilot score of 4.9 out of 5.
    • Gas Safe Accredited (corgi registered).
    • Very competitive Prices.
    • Finance is FCA accredited.
    • Well keep your house clean and tidy during any work because we care.
    • Floor protection used on each job.
    • All rubbish always disposed of correctly.
    • The Service comes with a 12-month snag guarantee.

    You can research your boiler replacement requirements and choose your new boiler and the boiler installation online, without leaving the house…

    Award winning engineers

    If you need a new combi boiler or heat pump and installation, please do not hesitate to reach out to our award-winning heating engineers team because they have all of the information that you will need.

    When you’re ready for a new boiler or heat pump then you can get everything from us because we know you’ll be extremely happy with our services.

    This includes services like; the full boiler supply, the full boiler fit and regular maintenance.

    All from Let’s Heat in Wales.

    Next Day Service

    We replace & install boilers and heat pumps nationwide and include next-day installation.  This is  on orders placed before 2pm in Spring/Summer or 12pm in Autumn/Winter*.

    *This needs to be slightly earlier in the autumn/winter because things are a bit busier during these months.


    All our staff are experienced and knowledgeable in all aspects of heating installation services and repair/maintenance.

    If you have any further questions please feel free to contact us.

    Alternatively please take a look at our FAQS or blog, should you have any other questions.

    Full range of heating & plumbing services provided by Let’s Heat:

    • Boiler Repairs & Installations
    • Boiler Supply & Fit
    • Financing Your Boiler
    • Emergency Boiler Repairs & Installations
    • Emergency Boiler Supply & Fit
    • Plumbing Repairs
    • Bathroom Plumbing
    • Kitchen Plumbing
    • Emergency Plumbing Repairs
    • Bathroom Plumbing in Emergencies
    • Emergency Kitchen Plumbing
    • General Plumbing Services
    • Emergency Plumbing Services
    • Emergency Gas & Heating Engineer

    Any more questions?

    If you have any further questions about boiler efficiency, other boilers, or anything else, please see our FAQ Page because you might find the answers there.

    Alternatively, you could try our News Blog for lots of news and article on all aspects of plumbing and heating.

    Check out our Gas Safe Registration and if you want to see our near 5 star Trustpilot rating, please click the relevant link because you can then find what you are looking for.

    Get a quote today because you don’t want to miss out on our exceptional value for money offering!


    What type of boiler is cheapest to run?

    Generally speaking, gas boilers are less expensive to run.

    Is a high efficiency boiler worth getting?

    A high efficiency, gas-fired condensing boiler is among the best economical and clean ways to heat your home, reduce your heating bills, and finally lessen the impact on the environment.

    What is a good efficiency rating for a boiler?

    The AFUE rating for an all-electric furnace or boiler is between 95% and 100%.

    How much does an energy efficient boiler cost?

    the cost of a boiler varies between £500 – £2,500, depending on the system, size and model.

    How long do high-efficiency boilers last?

    around 15 years.