James Elston

Published April 9, 2024

Green boilers are quickly emerging as an eco-friendly replacement for traditional gas boilers. These boilers are considered “green” because they maximise the energy they use to create heat, thus reducing their environmental impact. 

Electric, biomass, condensing, and hydrogen-ready boilers are typically considered green boilers thanks to their great energy efficiency. 

While “traditional” gas boilers have long been the popular choice for heating homes, their negative impact on the environment and inefficiency requires a shift to greener alternatives.

Additionally, new regulations aim to phase out gas boilers by 2025, making eco-friendly solutions even more important.

In this article, we’ll take a deep dive into green boilers to understand their functioning, costs, benefits, and challenges. 

Understanding Green Boilers

Green boilers are eco-friendly heating solutions designed to reduce their harmful impact on the environment. These versatile boilers can use renewable energy fuels and incorporate heat recovery technology to reduce energy waste.

Unlike non-condensing gas boilers, they have higher efficiency ratings. This means these boilers are more efficient at converting fuel into heat energy. Traditional boilers – those running on oil or gas – lose heat through flue gas or by releasing it into the air.

For instance, a green boiler with an efficiency rating of 94% will use this percentage of used fuel to generate heat, while only 6% will be wasted. Compare that to an inefficient boiler that operates at high temperatures and requires more fuel to produce the same amount of heat.

Overall, a green boiler is beneficial to the environment as it reduces greenhouse gas emissions that are released into the atmosphere. Because they use less fuel, these energy-efficient boilers save costs all around.

How a green boiler works

A green boiler draws heat from the ground, air, or water to provide your home with hot water and meet its heating needs.

Excess energy from the power grid can be stored and used as thermal energy to generate electricity when necessary.

Before purchasing a new boiler, it is vital to understand the Energy-related Products systems (ErP). The ErP system uses letters A to G to rank the efficiency of a boiler.

A+++ is the most efficient rating, while G is the lowest. The percentage accompanying the letters represents the boiler’s efficiency in converting fuel energy into heat. You should find a sticker on your boiler with one of these ratings, displaying how efficient it is.

  • A: 90% or more
  • B: 86-90%
  • C: 82-86%
  • D: 78-82%
  • E: 74-78%
  • F: 70-74%
  • G: below 70%

Green boilers vs traditional models

There are several significant differences between a green boiler and a model that burns fossil fuels.


Green boilers are A-rated, meaning they are 90% or more efficient at converting the fuel they use to create steam and heat. Condensing boilers can even reach up to 99% efficiency!

Non-condensing boilers, on the other hand, lose heat by releasing it into the air through flue gases, reducing their efficiency to around 70% to 80% (F to D rating). 


Green boilers are often more expensive to buy and install, thanks to their advanced internal mechanisms and complex machinery. When it comes to long-term maintenance, green boilers can also be costly to maintain due to their many moving internal parts. 

However, they are known to last longer than traditional models, giving you more value for your money. Plus, you’re guaranteed to save money on your energy bills due to their superior efficiency. 

Traditional boilers are the cheaper alternative when it comes to installation and maintenance costs. This is due to their simple makeup, which makes installation and repair work much easier. However, you can expect to replace your boiler more frequently as well as contending with higher energy bills. 

Government incentives

The UK Government currently provides a grant to cover the partial cost of replacing a fossil fuel boiler (including traditional boilers) with a heat pump or biomass boiler (a type of green boiler), under the Boiler Upgrade Scheme

This initiative is aimed at making eco-friendly heating solutions, like biomass boilers, more accessible to the public. 

Conversely, the government is implementing a gas boiler ban by phasing out the installation of traditional gas boilers in new builds by 2025. This is due to their environmental impact and poor efficiency. 

Environmental impact

Thanks to their high energy efficiency, green boilers have less of an environmental impact. Using almost all of the fuel or energy they consume to produce heat, they minimise waste and produce little to no carbon emissions while operating. 

The opposite is true for traditional boilers. They waste more energy and release a high level of carbon dioxide through the combustion process. 

For example, a non-condensing traditional boiler emits an average carbon footprint of around 8 tonnes of carbon dioxide per year, while a condensing boiler has a footprint of around five tonnes. Additionally, electric boilers don’t release any carbon dioxide while in operation. 

Types Of Green Boilers

There are three green or eco-friendly boilers on the market, each with advantages and disadvantages.

Electric boilers

Electric boilers use only electricity, meaning they don’t require “traditional” gas combustion but work similarly to a kettle. This boiler draws cold water from the main supply to a heating element, which then warms the water circulating through radiators and can be used via the taps.

Electric boilers help reduce our carbon footprint by using electricity directly.


  • This type of boiler has fewer moving parts, so it is much quieter.
  • They are cheaper and quicker to install since they do not have a flue.
  • Electric boilers are generally safer than gas boilers since there is no risk of a gas leak. 
  • No emissions are produced during the heating process.
  • They generally take up less room than gas boilers, making them space-savvy. 


  • An electric boiler relies on a consistent electricity source. The boiler will not produce hot water if there is a power outage.
  • This type of boiler is usually much smaller and is not recommended for mid-size or larger homes.
  • This boiler can be more expensive, and expenses might increase depending on the electricity charges in different regions.

Biomass boilers

A biomass boiler burns natural materials (such as wood pellets or agricultural waste) for heating. This renewable source of energy is one of the most eco-friendly and green options.

When organic materials are burned, it releases carbon dioxide (CO2). However, the effect it has on the environment is negligible, making this type of boiler carbon-neutral. It emits 230 grams of CO2 per kWh throughout its entire lifecycle.


  • Biomass boilers are often cheaper to run than the traditional system or combi boilers.
  • These boilers are considered carbon-neutral, which means that the amount of CO2 they release is limited enough to be re-absorbed by growing plants.
  • If you want to install a biomass boiler you should qualify for the Renewable Heat Incentive (RHI) Scheme.


  • These boilers have a much larger system, so they require more space.
  • A biomass boiler must be cleaned at least once a week.
  • This specific boiler is more expensive and can cost from £4,000 – £8,000.

Condensing boilers

A condensing boiler is designed to recycle heat from flue gases and extract heat from the burning process. The advanced condensing technology allows them to achieve exceptional levels of efficiency.

Recycling heat is a great way to reduce waste and help create a more environmentally friendly world. A condensing boiler uses less fuel and produces fewer carbon emissions.


  • Condensing boilers are far more energy-efficient than non-condensing boilers. Some models have an ErP rating of 98%, resulting in low heating bills.
  • A condensing boiler is typically compact and can be mounted on the wall.
  • These boilers have a longer lifespan, are compatible with fossil fuels and natural gas, and are more fuel-efficient.


  • These boilers have higher installation costs.
  • Some condensing boilers have aluminium heat exchangers or inners. These metal elements are prone to rust and corrosion because they are exposed to acidic wastewater.
  • The condensate pipes are prone to freezing and could even burst in icy weather.

Hydrogen-ready boilers 

A hydrogen-ready boiler is a type of gas-fired boiler that is capable of using both gas and hydrogen to produce heat. While hydrogen gas is not readily supplied by the mains gas network in the UK, it is being looked into as a feasible replacement for natural gas. 

Hydrogen does not produce any carbon dioxide when it’s burned, which is why this type of boiler is classified as “green”. 

While you can’t currently purchase a 100% hydrogen boiler in the UK, you can buy a hydrogen-blend-ready boiler. These boilers are capable of running on 20% hydrogen and 80% natural gas when or if the switch to hydrogen occurs. 


  • Hydrogen only produces heat and water when it’s burned, meaning it does not release any harmful carbon emissions into the environment. 
  • Hydrogen boilers promise to be more energy efficient than traditional gas boilers, considering that 1 kg of this gas produces the same amount of energy as 2.8 kg of natural gas. 
  • The production of hydrogen can be more sustainable than that of natural gas since it can be made using wind and solar power. 


  • These boilers are currently not available for purchase in the UK. While you can get a hydrogen-blend-ready boiler, 100% hydrogen boilers are still in the development phase. 
  • Since hydrogen boilers are a relatively new concept, their purchasing costs are expected to be much higher than any of the other green boilers we’ve mentioned. 
  • Hydrogen is highly flammable, which presents safety risks when it comes to installation and maintenance. 

The Costs of Green Boilers

The installation, running and maintenance costs of a green boiler will vary depending on numerous factors, such as the: 

  • Make
  • Model
  • Size
  • Fuel requirements
  • Installation complexities 

However, we can look at the average costs associated with green boilers in the UK. 

Note: Since hydrogen-ready boilers are still in the development phase, we haven’t included their costs in this breakdown. 

Installation costs 

  • Electric boiler: £650 – £2,500
  • Biomass boiler: £4,000 – £21,000
  • Condensing boiler:  £1,000 – £3,000

Annual running costs 

  • Electric boiler: £500 – £1,500
  • Biomass boiler: Up to approximately £950
  • Condensing boiler: Around £1,200 – £1,500 

Annual maintenance costs 

  • Electric boiler: £60 – £100 
  • Biomass boiler: £180 – £450
  • Condensing boiler: £60 – £180

Green Alternatives Beyond Boilers

Beyond the green boiler, there are additional eco-friendly central heating system alternatives worth exploring, like a heat pump vs solar panels. Each alternative brings its own set of advantages and disadvantages, catering to different needs and preferences.

Solar thermal panels

Unlike conventional boilers, solar thermal panels absorb sunlight to heat water directly. The water is then stored in a hot water cylinder for use in the home and space heating.

Solar thermal panels have several benefits. One advantage is that these panels can generate a constant energy supply and can operate without interruption.

Although solar panels cost more upfront, they have low operating costs, making them cost-effective in the long run. One disadvantage is that their effectiveness changes depending on the weather conditions.

Heat pumps (ground source and air source)

A heat pump is a device that takes heat from the ground or the air to heat a room. Instead of burning fuel, they work by transferring heat.

The difference between an air source heat pump and a ground source heat pump is how it absorbs heat:

  • Air source heat pumps draw heat from the air outside.
  • A ground source heat pump uses pipes (ground loops) to draw heat from the ground.

Heat pumps are far more effective at turning extracted heat into usable warmth. They can be used for both heating and cooling.

The disadvantage of a heat pump is that it relies on electricity. Air and ground source heat pumps take longer to heat up than gas boilers and do not work well in colder temperatures.

Benefits Of Upgrading to a Green Boiler

Transitioning from a conventional gas or gas combi boiler to a green boiler offers many benefits. Not only does it help to conserve the environment, but it also carries financial incentives.

Savings on heating bills

Green (or “greener”) boilers allow for optimal heat generation, providing exceptional energy efficiency. Installing one can significantly reduce your energy and heating bills.

Longevity of green boilers

These boilers have a longer lifespan than older boilers that run on oil or gas. A condensing boiler can last for 15 to 25 years, biomass boilers last for 20 to 25 years, and an electric boiler’s lifespan is 20 to 25 years. This reduces the frequency of replacing your boiler and is a more sustainable heating solution.

Reduced carbon emissions

Installing a green boiler means that you are actively contributing to an eco-friendly environment. These boilers produce significantly lower carbon emissions – an essential step toward the target of net zero emissions by 2050.

Many homes are working towards using renewable electricity sources in general, such as relying on solar panels for power.

Quicker heating

This kind of boiler uses less energy, leading to faster heating and a more efficient turnaround. For instance, a green boiler can save up to 1,220kg of CO2 annually compared to its conventional counterpart. They require less energy to generate more heat and draw energy from renewable sources.

Challenges In Transitioning

While the benefits of installing a green boiler are clear, transitioning has a few challenges, especially for homes with a gas heating system.

Feel free to contact Eco Happy – we’ll help you explore all the alternatives to gas boilers.

Gas heating system

When transitioning to a green boiler with existing gas central heating, there are a few important factors to consider to ensure everything goes smoothly.


Check that your existing heating system, including the pipes and connections, is compatible with the green boiler of your choice. This would include looking at the size of the pipes used for water circulation. If there are any compatibility issues, your new boiler might not work effectively.


A condensing boiler has specific requirements for proper combustion and heat exchange. You need to ensure that the installation location allows enough airflow according to the manufacturer’s ventilation specifications. Also, check if your new green condensing boiler needs a particular type of flue or modification to your existing system.

Balancing additional costs

Besides saving on energy, you can consider different ways to reduce financial costs. Accessing low-interest loans or government schemes gives you financial flexibility without having to spend a lot of money upfront.

The Boiler Upgrade Scheme will help you pay for the installation of low-carbon heating systems like heat pumps or biomass boilers. You could receive a grant of up to £7,500 for a heat pump, or £5,000 for a biomass boiler.

The Boiler Upgrade Scheme will be accessible in England and Wales until 2028.

Heat output 

Since green boilers are more efficient, they generally produce a better heat output compared to non-condensing, gas boilers. 

However, when it comes to electric vs gas heating in large homes, gas boilers often come out on top. Gas boilers are usually better able to meet your hot water and heating demands, especially compared to an electric combi boiler

Green Deal Scheme

The Green Deal Scheme is a government program intended to assist landlords and homeowners in England, Scotland, and Wales in making energy-efficient home upgrades.

One advantage of the scheme is that the loan enables households to finance improvements, like insulation, double glazing, and installing carbon-neutral heating systems.

The concept of the scheme is simple. The cost of the Green Deal loan should not be higher than the energy you save. In other words, your expenses should not increase but rather decrease your energy bills.

To apply for a loan, you must have your property assessed by a registered and authorised assessor who will provide recommendations for energy improvements.


Is LPG a green fuel?

LPG (or liquefied petroleum gas) is considered an environmentally friendly source of energy. Although it is a fossil fuel, it is a cleaner energy source that emits minimal pollutants.

What is an eco-boiler?

An eco-boiler is designed to prioritise the environment and save energy. Its operation relies on renewable energy sources, like trees, instead of fossil fuels.

Are hydrogen-ready boilers really green?

Hydrogen gas emits no carbon and is suitable for hydrogen boilers and cookers. However, a recent investigation by Sky News pointed at deceptive greenwashing tactics. The channel found evidence suggesting that most gas boilers are not equipped to handle hydrogen gas.


A green boiler is the way forward if you are looking for an alternative to a gas boiler – no doubt about that. Transitioning to eco-friendly boilers ensures a sustainable and ecologically aware future. These boilers have several advantages, including reducing the UK’s total carbon emissions and more efficient household heating.

If you are ready to make the switch, contact us at Eco Happy for a personalised quote. We’ll guide you through the most energy-efficient boilers on the market so you find what works for you!

James Elston

Boiler Expert

James Elston is the top boiler replacement and heating expert at Eco Happy. He has over 20 years of experience in the industry, focusing on Gas Safe boiler installations and offering home-heating and energy-saving solutions to homeowners across the UK. From sourcing the most energy-efficient combi boiler to providing specialist heating advice, James ensures that Eco Happy maintains the highest standards and best customer service.

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