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Home & garden.

Updated: 25 Feb 2022

Hydrogen boilers: everything you need to know

Hydrogen has been hailed as the 'green' gas that could be heating our homes in the future. We explain how hydrogen boilers work, the potential costs, and the pros and cons of hydrogen as a fuel.
Sam Morris

Heating homes accounts for 17% of UK carbon emissions. To reach net zero by 2050, how we heat our homes is set to dramatically change over the next few decades, with a move away from traditional gas heating systems.

Some low-carbon heating systems, including electric boilers and heat pumps, are already available. But these have limitations. Heat pumps, for example, are disruptive to install and simply not practical (or even possible) for many households. Where they are viable, they're often prohibitively expensive (even allowing for financial support that will be available from April 2022). 

However, as the deadline to get heating net zero gets closer, more low-carbon technologies are likely to appear on the market. One of the solutions we expect to see take off is hydrogen. 

It's a low-carbon alternative to traditional gas (which is known as natural gas) and, because it's also a gas, could in theory be distributed using the same network. As most UK homes (85%) are already connected to the gas network, this could make hydrogen boilers a lower-cost, low-disruption alternative to an existing gas boiler. In this guide, we highlight what the future may hold for hydrogen-based heating. 

Need to replace your current boiler sooner than later? Read our boiler reviews to find the most reliable boiler brands

Video: hydrogen heating – future fuel or throwback? 

What are hydrogen boilers?

Hydrogen boilers work exactly like current gas boilers, except the fuel is hydrogen instead of natural gas.

Hydrogen is the most abundant element. When it burns in pure oxygen, the only thing released is water. 

Air isn't pure oxygen, though, so using hydrogen as fuel in homes isn't quite this clean. While there will be no carbon emissions, burning hydrogen will still produce some of the other pollutants that are a by-product of burning natural gas, such as nitrogen oxides (NOx), a group which includes the gas nitrogen dioxide (NO2).

NOx emissions are greenhouse gases, and contribute to climate change. Long-term exposure to high levels of nitrogen dioxide can also lead to increased respiratory harm. It's possible to manufacture hydrogen boilers in a way that minimises NOx emissions, but regulations would need to established to ensure this happens by default.

The need to create new regulations and procedures to mitigate unintended consequences and ensure that hydrogen boilers are safe and viable is part of the reason that they are not yet available. If and when these problems are addressed, and assuming hydrogen can be delivered to homes through the existing natural gas network, hydrogen boilers could be a low-cost, low-disruption option for many households. 

If you need a new natural gas boiler, find out how to get one with the least environmental impact using our guide on the most energy-efficient gas boilers.

Pros and cons of hydrogen boilers

As with all low carbon technology, hydrogen boilers will be a good option for some households, but not others. 

As a general rule, heat pumps better suit homes that are energy efficient and well-insulated. From 2025, all new homes will have to be built with a low-carbon heating system installed. In such new properties, where the planning can take account of relevant costs and infrastructure, heat pumps are likely to be a good option. 

However, retrofitting heat pumps into older properties with different heating systems can be costly and disruptive. In these cases, a hydrogen boiler is likely to be a far less intrusive option, and allow insulation upgrades to happen at a later date.

One thing that's not yet certain is how the running costs will compare with alternatives. As of early 2022, electricity prices are extremely high due to market factors pushing prices up, so if hydrogen boilers were a reality right now they'd probably be cheaper to run than electric boilers. However, this may not be the case forever.

Hydrogen boiler pros

  • Familiar technology – a hydrogen boiler will be easy for homeowners to understand and use.
  • Low disruption – the existing infrastructure could be utilised, meaning hydrogen-ready boilers could be installed before any switchover.
  • Reasonable upfront costs – likely to be more affordable to install than other solutions (such as heat pumps), based on current prices. However, we expect heat pumps to come down in price as their popularity increases. 
  • Can heat poorly-insulated homes – boilers can more effectively heat poorly insulated homes compared with heat pumps, so could provide homes to with a low-carbon option in advance of paying for expensive insulation upgrades.

Hydrogen boiler cons 

  • Hydrogen production isn't carbon-free – while burning hydrogen to provide heat doesn't create carbon emissions, certain methods of producing hydrogen do release carbon (see 'How hydrogen is produced', below). Truly green hydrogen is possible, but it's expensive and needs 100% renewable electricity.
  • Burning hydrogen produces other pollutants – such as nitrogen oxides. It's possible to control these and keep them to a minimum, but legislation needs to be put in place to ensure these controls exist in all hydrogen boilers.
  • Running costs likely to be higher than natural gas – hydrogen costs more to produce than natural gas, so it is likely hydrogen will initially be more expensive per kWh. Costs should come down as technology matures and hydrogen gets cheaper to produce, though.
  • There are unanswered questions – the government hasn't yet decided on how big a role hydrogen should play in heating homes in the future. This uncertainty might affect things such as the cost of hydrogen (or hydrogen-ready) boilers.

Part of the reason for the lack of clarity over the role hydrogen will play in domestic heating is that other sectors may need hydrogen more, especially while supply is relatively scarce.

The need for decarbonisation is far wider than in our homes. Industries such as aviation, shipping and steel, where electricity is not an option, will need solutions such as hydrogen to replace natural gas as their primary fuel.

Given that electricity is a viable solution to heat homes, some argue hydrogen should therefore play a smaller role in heating homes than natural gas currently does.

If your next boiler is gas or oil, read our shortlist of the best boilers to make sure you get a model from a reliable brand. 

When will hydrogen boilers be available?

composite image of worcester bosch and baxi hydrogen boiler prototypes

There is currently no set date, but it is likely that hydrogen-ready boilers will start appearing on the market in the next few years. 

Boiler manufacturers have already built prototypes for hydrogen boilers, with many calling for legislation to make it law that all new gas boilers sold from 2025 onwards must be hydrogen-ready.

There are still logistical questions that need to be answered before hydrogen boilers can come to market, the two biggest being:

  1. Can hydrogen be passed through the existing gas network?
  2. Can we produce enough 'green' hydrogen (see see 'How hydrogen is produced', below) at scale?

The government is set to make a decision on the role hydrogen will play in home heating by 2026.

What are hydrogen-ready boilers?

Like 'HD-ready' was to televisions before there was any HD content to view, hydrogen-ready boilers can run on the existing natural gas supply and, when it becomes available, be easily converted to run on 100% hydrogen. 

This would allow hydrogen-ready boilers to be installed in homes before any switch from natural gas to hydrogen happens. This will cause far less disruption, and ensure households only need to replace their boiler when it breaks. 

The idea is that if and when your area gets switched from natural to hydrogen gas, an engineer will come and carry out a service on your hydrogen-ready boiler to convert it to run on hydrogen. This service should take about an hour and the industry is anticipating it will cost about £100.

This type of roll out will require all households to have a hydrogen-ready boiler in advance of the switch, so that nobody is left without heating because their boiler isn't suitable for hydrogen. The logistics of this will need to be taken into account when drawing up these plans.

How much will a hydrogen boiler cost

A number of leading boiler manufacturers have made a joint price-promise commitment that a hydrogen-ready boiler will cost no more than a gas boiler does today.

However, economies of scale means that this depends on the level of demand being as great as it currently is for gas boilers. Until the government decides on just how big a role hydrogen will play in heating our homes, and hydrogen-ready boilers start to appear on the market, we can't be certain on the price.

We do expect that upfront costs – for the boiler itself and installation – will be closer to that of a gas boiler (typically around £2,500 for a like-for-like combi-boiler replacement) than to the current price of a heat pump (typically £8,000 to £14,000). However the cost of heat pumps (including installation) is expected to fall, with the aim for it to be comparable to gas boilers by 2030.

How much does a new boiler cost? – find out how much you should expect to pay for different types of gas or oil boiler. 

What is blended hydrogen?

At present, domestic hydrogen heating is a pipe dream (no pun intended). While we are using natural gas, there's no consumer demand for hydrogen, which in turn means little hydrogen is produced. But if hydrogen isn't produced, how do we use it to decarbonise heating? It's a bit of a chicken-and-egg scenario. 

One solution, to help unlock this stalemate and catalyse hydrogen production, is introducing hydrogen in a small quantity to the existing gas supply. 

Dubbed 'blended hydrogen', this concept would involve mixing 20% hydrogen with 80% natural gas. All existing gas appliances are certified to run on a 23% hydrogen-blend, so introducing a mix at this proposed level would reduce carbon emissions by about six million tonnes a year (equivalent to taking 2.5 million cars off the road) without anyone having to replace their current gas boiler or appliances. 

Hy Deploy Project

The Hy Deploy project is currently testing the feasibility of injecting hydrogen into the gas network. The first trial at Keele University was completed with no issues. 

As part of this first trial, two identical boilers were run continuously – one on natural gas, one on blended hydrogen – to simulate 12 years of use. No difference in how each boiler operated was observed.

The second stage of the trial has seen around 650 homes in Winlaton, a village in the North East of England, receiving blended hydrogen from August 2021. To date, there have been no issues. 

The results of this project will feed into the governments final policy decision on blended hydrogen, which is due in 2023.

Blended hydrogen pros

  • Reduces home carbon emissions without the need to replace existing gas boilers and appliances.
  • Helps open up the market for hydrogen by creating a demand for hydrogen production.

Blended hydrogen cons

  • Only a maximum of 20% hydrogen can be introduced to the gas network without the need for gas boilers and appliances to be replaced.  
  • Blended hydrogen reduces, but doesn't eliminate carbon emissions from the home. As such it is at best a short-term solution and a stepping stone on the path towards Net Zero. 

Hydrogen heaters and appliances

A switch to hydrogen won't just mean replacing your natural gas boiler; you'll also need hydrogen versions of all your gas appliances, such as cookers and stoves.

Prototypes of such appliances have been produced and are currently being showcased in two semi-detached homes in Gateshead. Built in partnership between gas distributors Cadent and Northern Gas Networks (NGN) and the Government’s Department for Business, Energy and Industrial Strategy (BEIS), it provides the public with the opportunity to experience a zero-emission, gas-fuelled home of the future. 

Which? visited these hydrogen homes in October 2021 to see what the fuss is all about.

Hydrogen cookers and hobs

Before they're turned on, the hydrogen cooker and hob on display look no different to their natural gas equivalents. When in action, though, there are a few differences, including:

  • Flame colour With natural gas cookers and hobs, the normal flame colour is blue; an orange or yellow flame is a bad sign, indicating inefficient burning and higher carbon emissions. However a healthy hydrogen flame is a sunny yellow/orange.
  • Hydrogen flames give off less sideways heat Whereas the flame on a natural gas hob is hot all around, a hydrogen flame is significantly cooler at the sides of the flame than above it. Hydrogen gas rises quicker and has less radiant heat than natural gas. This is good for cooking on a hob, as a hydrogen flame gives out less heat to its surroundings, and more of its heat is transferred the pan directly above it.
  • Popping sound on ignition Similar in volume to the pops you get if it takes your cooker a while to ignite natural gas, this pop is nothing to worry about. It comes from the sound of hydrogen igniting, and simply indicates that your hydrogen boiler has lit. In fact the 'squeaky pop' is the test for hydrogen gas in school science lessons.

The prototype hydrogen cookers also have a safety feature, so the grill turns off if the cooker door is closed. And hobs have LED indicators to show you if a burner has been accidentally left on.

Hydrogen is naturally odourless but, like natural gas, would have an odour added to it if supplied to public homes. This is so you can smell the gas and spot a leak.

Hydrogen fireplaces and sensors

Besides the 'squeaky pop' sound on ignition, the prototype hydrogen gas fireplace looks and feels exactly like a natural gas fireplace.

The prototype fireplace lights the room with a warm orange glow and it pumps out a lot of heat, quickly warming the room it's in.

Hydrogen sensors work like carbon monoxide alarms to detect a hydrogen leak. Hydrogen mixes readily with air, and if able to accumulate in a confined space without being detected, can make this air ignitable.

Unlike carbon monoxide alarms, hydrogen sensors must be installed on the ceiling, because hydrogen – the lightest element – rises in air.

How hydrogen is produced

The potential benefits of hydrogen boilers are clear, but there are outstanding questions around how the hydrogen itself will be produced: 

How is hydrogen made?

Hydrogen can be produced in a number of ways, some of which are more environmentally-friendly than others, as the most common processes create carbon emissions during production. Different colour designations are used to indicate how a specific batch of hydrogen was made. 

Grey hydrogen

This hydrogen is made by reforming methane or natural gas. Carbon dioxide is produced during this process. It's currently the most common way of making hydrogen, and has the highest carbon emissions.

Blue hydrogen 

This uses the same process as grey hydrogen but the majority of the carbon dioxide is captured and stored before it’s released into the atmosphere.

The amount of carbon that is prevented from being released into the atmosphere varies, and depends on the quality of the carbon capture and storage systems used. The methods analysed in the Government's 2021 paper on hydrogen production costs claimed to be able to capture 90 to 96% of carbon emissions.

Currently, it is the easiest way to produce hydrogen that has lower carbon emissions than grey hydrogen. However, blue hydrogen isn't zero-carbon. 

And, like grey hydrogen, its production relies on natural gas. Because of this, many believe the focus should be on a greener long-term production method that doesn’t require natural gas: electrolysis.

Green hydrogen

Green hydrogen is made by splitting water using electricity. While this production method doesn't require natural gas, it's only zero-carbon if the electrolysis process is powered entirely by renewable electricity. 

However, this is currently expensive to do and will remain so until the UK's electricity comes mainly or solely from renewable sources. The Scottish government's 2020 hydrogen assessment predicts that, as green hydrogen matures, it could compete with blue hydrogen by the mid-2030s.

However, it is likely that green hydrogen, in the short-to-medium-term, will be more expensive per kWh than natural gas is today.

Turquoise hydrogen

Research into so-called 'turquoise' hydrogen by hydrogen technology company HiiROC uses a process called thermal plasma electrolysis to produce hydrogen from methane and natural gases, but with solid carbon as the waste product, rather than carbon gases. 

This solid carbon (also known as carbon black) can then be used for other purposes, such as enhancing soil or used in tyres and building materials.

How much hydrogen do we need to produce? 

It’s predicted that a nine to seventeen-fold increase in hydrogen production will be needed by 2050 to meet demand, according to the government's Heat and Buildings Strategy.

The UK currently produces about  27 terra-watt hours (TWh) of hydrogen a year. That means, to meet anticipated demand, it will need to be producing 250 to 460 TWh a year by 2050.

A key factor in determining whether production will need to be at the lower or higher end of this spectrum is exactly how many homes (if any) will be using hydrogen for heating. But either way, scaling up production over the next 30 years will be no small task.

What about homes without a gas supply?

Air source heat pump outside a home

In its 2021 Heat and Buildings Strategy, the government has proposed regulation to phase out fossil-fuel heating in homes that are off the gas grid from 2026. This is in the anticipation that most home owners will install a heat pump the next time they need their current heating system replaced.

The report indicates that 80% of homes are energy-efficient enough for a heat pump to be a suitable heating method. Find out more about what's involved in installing a heat pump with our expert advice on air source heat pumps and ground source heat pumps.

Another option for homes with no access to gas could be an electric boiler. Read our guide on electric boilers to find out if this would be a suitable solution for you.