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Best Green Boilers


Gas boilers have been the primary heating solution for most UK households for many years. However, despite its popularity, natural gas heating is associated with high energy bills and severe environmental impact due to high carbon emissions. With such serious concerns surrounding gas heating, more households are moving away from gas-powered heating systems and adopting more cost-effective and environment-friendly heating solutions.

This guide explores some of the best eco-friendly heating systems that you can install in place of your gas boiler. All the solutions mentioned in this guide have attained a balance between

What is a green boiler?

A green or eco-friendly boiler is a highly efficient heating system that produces little to no carbon emissions during its production process or when in operation. The “greenness” of a boiler is measured by its efficiency at converting fuel into heat. As such, it is expected that some heating systems would be “greener” than others.

Although green boilers should ideally run on renewable energy sources, not all do, as some still run on fossil fuels. It is, however, essential to note that the high efficiencies of fossil fuel-powered green boilers ensure that 98% of the burnt fuel is converted to usable heat.

How is the eco-friendliness of a green boiler determined?

Several factors determine the eco-friendliness of a green boiler. Some of these factors include:

  • Energy efficiency: Energy efficiency refers to the ability of a boiler or heating solution to produce usable heat with the least possible energy wastage. Boilers are usually allocated ErP ratings, with the highest one being 100. An ERP rating of 100 means the boiler can convert all the fuel to usable energy. Similarly, an ERP rating of 90 means 10% energy is lost between the combustion of the fuel and the production of usable energy.
  • “Cleanliness”: Cleanliness in this context refers to the pollution levels that a boiler releases when it burns fuel to produce steam. The pollutants, in this case, are greenhouses gases, mainly CO2 and NOx. Boilers with low greenhouse emissions are considered greener than those that release more CO2 and NOx gases.
  • Nature of fuel: Heating solutions that run on renewable energy are considered greener than fossil fuels. However, it is worth noting that although most condensing boilers run on unrenewable fossil fuels, they can reclaim some of the waste heat. This loosely means that these boilers can “renew” some of the energy they use.
  • Carbon neutrality: Carbon neutrality refers to the ability of a boiler to release the same amount of carbon that the fuel source absorbed when being formed. A biomass boiler is considered carbon neutral since it emits the same amount of carbon dioxide that the wood pellets absorbed while growing up.

Best Green Boilers

Here are some of the greenest boilers with their advantages and disadvantages. It is important to note that the list includes some green heating systems, which although not necessarily in the boiler category, can be installed as replacements for gas boilers.

Condensing Boilers

Although they run on fossil fuels, modern condensing boilers have what it takes to make it to the list of best green boilers. These boilers operate in a similar way to older, non-condensing boilers. They burn natural gas or oil to produce heat and release some level of CO2 gas in the process.

However, unlike their old, non-condensing counterparts, condensing boilers have a Flue Gas Heat Recovery System (FGHRS) that recycles the hot waste flue gases from the combustion process. The recovered hot flue gases are used to heat the cooler pipework in the boiler, thereby minimizing the amount of fuel used in heating the water in your boiler system.

The FGHRS enables the condensing boiler to produce more heat from the oil or gas fuel they burn. It also minimizes the amount of fuel and heat wasted during the heating process. And with lower fuel consumption comes lower carbon emissions. Trading your old, non-condensing boiler for a modern condensing one will decrease your annual CO2 emission by 1,220 kg.

Some of the best green condensing boilers include:

  • Evoke series by Alpha
  • ecoFIT and ecoTec boiler ranges by Vaillant
  • Ideal Vogue series
  • Vitodens boiler range by Viessmann
  • Worcester Bosch 4000 and Greenstar 30i boiler range

Advantages of condensing boilers

  • They are highly efficient and can reach up to 99% efficiency, at least 21% higher than the newest non-condensing boilers. A condensing boiler will save you up to £310 in annual heating costs by capturing 11% more heat than a non-condensing model.
  • They have a lower carbon footprint and can lower your annual carbon emission by 1,200 kg.
  • They are more space-efficient and can fit into a standard kitchen cupboard.
  • They are safer as they are a perfectly sealed system.

Disadvantages of condensing boilers

  • They are prone to freezing in winter as the condensate pipe is exposed to harsh weather.
  • They are not entirely green as they run on fossil fuels
  • They are more complex to operate compared to non-condensing boilers
  • They have higher maintenance costs due to their complex systems

The cost of a new condensing boiler unit ranges between £500 to £1,700 depending on the brand and output rating.

Biomass Boilers and Stoves

Biomass boilers and stoves are heating systems that burn biomass fuels such as wood, logs, chips, and animal waste to produce heat. Biomass boilers are usually connected to a central heating system and supply a whole house with warmth and hot water. On the other hand, a biomass stove is an independent unit that is used to heat a single room.

Biomass boilers and stoves are considered carbon-neutral heating solutions since the carbon dioxide they emit by the combustion of wood is the same as that absorbed by the trees or plants while growing up. This makes them sustainable heating solutions with no negative impacts on the environment.

The UK government is fully endorsing biomass boilers and is even rewarding homeowners for installing them. As such, by heating your home using a biomass boiler, you could earn sizeable amounts through the government’s Renewable Heat Incentive programme.

Advantages of biomass boilers and stoves

  • Cheap fuel source
  • It is a carbon-neutral heating solution.
  • Provides an efficient way to use waste wood and plans
  • It is a practical heating solution for those living in remote areas

Disadvantages of biomass boilers and stoves

  • Biomass boilers are massive and can be up to 4 times larger than gas boilers.
  • They are expensive to install
  • They require intensive maintenance as ash and soot have to be cleaned from the system regularly.
  • They require extra space for storing fuel.

Biomass boiler units are expensive and cost between £5,000 and £13,000.

Electric Boilers

Electric boilers use electricity to heat water for central heating and domestic use. They are usually considered a green heating solution as they do not emit carbon into the atmosphere when they are in operation.

Most electric combi boilers have a 100% efficiency rating, meaning that all the energy they consume is converted directly to heat.

It is important to note that despite electric boilers having zero carbon emissions, they aren’t precisely carbon neutral since the electricity used to fuel these boilers is generated by burning fossil fuels. This means that although electric boilers may seem green on the surface, a closer look reveals that they indirectly contribute to carbon emissions.

However, with electric generation shifting to renewable sources such as solar, wind, and hydro, more green electricity is in the grid than ever before. This means you have to find an energy supplier that generates electricity from renewable sources, and your electric boiler will be 100% green.

Advantages of electric boilers

  • There are no carbon emissions as they heat your home
  • They are highly efficient and can reach 100% efficiency
  • It is a perfect heating solution for off-grid properties
  • They are easy and cheaper to install as they don’t have a flue pipe
  • They are silent while in operation
  • They don’t require mandatory annual servicing

Disadvantages of electric boilers

  • The cost per unit of electricity is high, making electric boilers expensive to run.
  • They aren’t efficient for high heating output, meaning it isn’t suitable for bigger properties.
  • They are affected by power cuts.

Electric boiler units typically cost between £1,500 to £4,500

Hydrogen Boilers

Hydrogen boilers are essentially gas boilers that burn hydrogen gas to produce heat. The first 100% hydrogen boiler is yet to hit the markets, but boiler manufacturers are currently working on it. The available hydrogen boilers are the hydrogen-ready boilers that burn a mixture of hydrogen and natural gas, usually in the ratio of 20:80.

Boilers that run on pure hydrogen will be 100% green as they have a zero-carbon output, burning hydrogen fuel to generate heat and water vapour. However, similar to electric boilers, the generation of the hydrogen fuel used to run these boilers isn’t entirely green and results in the emission of carbon. Researchers are, however, working on finding carbon-free hydrogen generation processes that will make hydrogen boilers green through and through.

Advantages of hydrogen boilers

  • Hydrogen is a highly efficient fuel and produces up to three times the energy produced by a similar unit of fossil fuels.
  • Hydrogen fuel is non-toxic, unlike nuclear energy and natural gas
  • Hydrogen energy is renewable and is inexhaustible
  • Hydrogen fuel is a clean energy source that has no carbon emissions
  • Hydrogen boilers can utilize the same infrastructure as those used by gas boilers

Disadvantages of hydrogen boilers

  • Hydrogen fuel is a highly volatile fuel due to its high energy content, making it risky.
  • Hydrogen fuel is expensive to produce
  • It is challenging to store hydrogen fuel
  • The production of hydrogen energy leaves a carbon footprint
  • Hydrogen boilers can produce NOx

The cost of a hydrogen boiler unit is yet to be known as they are yet to hit the market. They are, however, expected to cost the same as gas boilers.

Heat Pumps

Heat pumps are a relatively new heating technology that absorbs natural heat from the air outside your home or underground and uses it to heat water for central heating and domestic use.

There are two types of heat pumps: air-source heat pumps and ground source heat pumps. Both heat pumps are highly efficient and generate 3 to 4 times the same energy as conventional electric boilers while using the same amount of electricity.

Heat pumps are considered a clean and sustainable heating solution as they do not emit carbon as there is no combustion involved. Moreover, the natural heat they absorb from the surrounding air or deep underground is constantly replenished by the sun and will never run out.

Air source heat pumps (ASHPs)

Air source heat pumps draw air from outside your property and extract heat from it. The heat is then used to provide warmth and hot water for your home. They usually operate all year round and can extract heat from the surrounding air even when it is at a temperature of -25 degrees Celsius.

Ground source heat pumps (GSHPs)

Ground source heat pumps extract heat from the ground surrounding your home. It achieves this by pumping a mixture of water and anti-freeze fluid into the ground. The mixture of water and anti-freeze fluid extracts heat from the soil and is pumped back to the compressor, where the heat is amplified and used to heat water in a hot water cylinder.

Advantages of heat pumps

  • They are cheaper to run compared to gas and electric boilers
  • They have zero carbon emissions
  • They are highly energy-efficient, producing 3 to 4 times the energy they use in the heat generation process.
  • Air source heat pumps require little maintenance.
  • Some reversible models can cool your home during the hot summer months
  • They have a long lifespan and can last between 20 to 25 years

Disadvantages of heat pumps

  • They have high upfront costs
  • They have a lower energy efficiency when external temperatures are below 0 degrees Celsius.
  • Some air source pump models have noisy outdoor fans
  • They are not suitable for poorly-insulated properties
  • Installing a ground source heat pump is only possible if you have a garden
  • Installation of a ground source heat pump will disrupt your garden.

Air source heat pumps cost between £8,000 and £ 12,000. On the other hand, ground source heat pumps are more expensive and cost between £10,000 and £18,000 per unit.

Hybrid Heating Systems

Hybrid heating systems alternate between heat generated by a heat pump and a gas boiler. The heat pump is usually used in warmer months, while the gas boiler will kick in during cold weather when outside temperatures are too low for the heat pump to perform efficiently.

Advantages of hybrid heating systems

  • Lower carbon emissions than natural gas heating systems
  • They are highly efficient as they balance the eco-friendliness of a heat pump with the high reliability of a gas boiler
  • When installed with an air source heat pump, a hybrid heating system can cool your home during hot weather
  • It has a longer lifespan than a gas central heating system as the boiler is only used on freezing days

Disadvantages of hybrid heating systems

  • They are expensive to install
  • They aren’t as eco-friendly as other green heating solutions as they still use fossil fuels.
  • They require outdoor space for installation of the heat pump

A hybrid heating system is pretty expensive and costs between £5,000 and £10,000.

Infrared Heating Panels

Infrared heating panels utilize electricity to produce infrared energy used to heat solid objects and bodies in a room directly. They are highly efficient as no energy is wasted in heating unoccupied space.

Advantages of infrared heating panels

  • Lower carbon emissions compared to fossil-fueled heating solutions
  • They have low maintenance costs
  • They are silent while in operation
  • They take up little space and are portable
  • They are ideal for people with allergies as they do not disturb the air in the room.

Disadvantages of infrared heating panels

  • As they do not heat the air, the room will feel cold when the panels are switched off.
  • An infrared heating panel has a short-range and cannot effectively warm an object or person seated more than three metres from it.
  • They may not be effective if there are objects placed between the panels and the room’s occupants.

Infrared heating panels are an affordable heating solution, with a single panel costing between £150 and £500.

Solar Thermal Panels

Solar thermal panels absorb heat energy from the sun and use it to heat the water in your hot water tank. They are, however, not powerful enough to cater to the heating demands of a standard home and must be used together with heat pumps or infrared heating panels.

Advantages of solar thermal panels

  • They are eco-friendly as they use the heat from the sun
  • They require little maintenance
  • Solar thermal panels can meet up to 50% of a home’s hot water needs
  • They have low running costs

Disadvantages of solar thermal panels

  • They are affected by weather
  • They can’t be used as the sole source of energy in a home
  • They are not compatible with all heating systems
  • They are expensive to install.

Solar thermal panels cost between £5,000 and £7,000.

Why buy Green Boilers?

With domestic home heating contributing to about a fifth of the UK’s total carbon emissions, it is only natural that the fight against climate change would be brought into our homes. Therefore, the government is insisting that homeowners ditch heating solutions that run on fossil fuels and adopt ones that run on renewable or eco-friendly fuels. Eco-friendly heating solutions will release lower carbon emissions, therefore lessening the impact home heating has on the environment.

One of the items on the government’s 2050 carbon neutrality goals is eliminating the use of fossil fuels in households across the UK. And to achieve this, the government issued a ban on gas boilers in new-build homes from 2025 onwards. The ban on gas boilers could potentially extend to those already installed in properties, meaning it could soon be a requirement that all households must install green boilers.

There is also the issue that green boilers are more fuel and cost-efficient than most conventional boilers. To put this into perspective, your gas boiler is responsible for about 75% of your monthly heating cost. Around 80% of this comes from space heating, whereas the remaining 20% comes from hot water heating. With greener boilers being more efficient than regular boilers, you will be spending less fuel heating your home, which results in lower heating bills.

Additionally, as most green boilers run on renewable fuels such as solar energy and wood pellets, they are unaffected by the volatility of fossil fuels. This means installing a green boiler will future-proof you from potential price hikes resulting from dwindling natural gas and oil reserves.

Lastly, green boilers have fewer health and safety risks than conventional oil and gas boilers. For instance, there won’t be any risks of carbon monoxide building up in your home and causing serious health issues. Moreover, you won’t have to worry about fires or explosions caused by gas or oil leaks.

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