Hydrogen boilers: how they work and whether you need one
Many of us are aware that the amount of carbon dioxide being produced across the world is having an impact on the temperature of our planet. In the UK, our government is taking steps to ensure that we look after our planet and reduce CO2 production where possible.
As home heating accounts for a large percentage of your home’s carbon footprint, the government is looking at alternative ways you can heat your home that are more environmentally friendly. Currently, it offers grants towards the cost of heat pumps and other green home products (like solar panels) and it plans to ban petrol and diesel vehicles by 2035.
But something else that the government is looking into is hydrogen as a replacement for natural gas. Hydrogen is thought to be a cleaner alternative to methane (the current gas burned by gas boilers) because it doesn’t release carbon dioxide when it is burned. As carbon dioxide emissions are one of the main causes of global warming, it’s thought that by burning hydrogen instead, we could reduce the CO2 emissions that are a large contributing factor.
Hydrogen atoms can be found all over our planet – in water, in living things and in plants. However, to be collected as a gas, it needs to be manufactured from water using electricity.
Should this electricity be generated from solar or wind power (or other renewable sources), the hydrogen is considered 100% emissions-free.
While heat pumps are a great alternative to gas boilers that run using electricity, it’s nice to have choices, and a hydrogen boiler is another option for domestic heating. Below, we reveal what a hydrogen boiler is, as well as how it works (with a handy animation).
What is a hydrogen boiler?
A hydrogen boiler does what it says - it is a boiler that burns hydrogen as opposed to natural gas (or methane). It works in a similar way to existing natural gas boilers, burning the hydrogen via combustion to create hot flue gases that are used to heat the cold water. Once the water is heated up, it can be stored for later in a hot water tank or pumped around your radiators to increase the temperature of your home.
Hydrogen is a thinner gas than methane, so if your current boiler ran completely off hydrogen, there would be a high risk of gas leaks. For this reason, hydrogen boilers need to be specially adapted to reduce such risks and so their parts may differ, including the flame detector and burner (which we look at in more detail further down the page).
Hydrogen boilers shouldn’t be confused with boilers that use hydrogen fuel cells to work or with hydrogen-ready boilers, as these are different types of systems.
What is a hydrogen-ready boiler?
In contrast to both a hydrogen boiler and a boiler that uses hydrogen fuel cells, a hydrogen-ready boiler is an appliance that has the ability to burn both natural gas and hydrogen. This means that when the UK’s gas network is able and ready to switch from methane to hydrogen, you won’t need to replace your gas boiler.
The viability of this approach is still under early research and development, however it is expected to be one of the many methods of supporting overall decarbonisation. Solutions are being looked at to also see how currently qualified heating engineers may be able to support converting products that have been developed with this in mind.
When hydrogen can eventually be introduced into the gas network, it’s likely that it will be phased in, rather than switching from all natural gas to all hydrogen. A trial took place at Keele University as part of their HyDeploy programme. Between 2019 and 2021, they added 20% hydrogen into their gas supply to reduce the amount of natural gas being burned to around 80%, and the trial sufficiently fed 30 faculty buildings. If the same scheme was applied across the country, it’s thought that it could save up to six million tonnes of CO2 every year.
When will hydrogen boilers be available?
This all sounds perfect, right? A more cleanly burning fuel that could reduce the planet’s CO2 emissions?
Unfortunately, the technology is still being developed and there are no boilers available on the market that can run with 100% hydrogen. Viessmann, however, is one of the first manufacturers to develop a hydrogen-ready boiler that has the potential to operate using 100% hydrogen. The prototypes are currently being tested in Germany.
How do hydrogen boilers work?
Now that we know what hydrogen boilers are and how they differ from hydrogen-ready boilers, how exactly does this technology work?
1: Oxygen and hydrogen enter the boiler
Firstly, oxygen and hydrogen enter the main boiler unit. The hydrogen will come from the main gas supply when this is an option and the oxygen will come from the air. The gas inlet contains a valve that controls how much of each gas can enter the boiler. This is important as the amount of gas can impact the size of the flame.
2: The gases are mixed and burned
The hydrogen and oxygen gases are mixed together before being ignited in a catalytic burner. Hydrogen is more flammable than natural gas and so the burners on hydrogen boilers are specially designed so that the flames can be limited if too much gas is flowing through. A flame detection component is also required in a hydrogen-only boiler as hydrogen flames are invisible.
3: The hot gases enter the heat exchanger
Hot flue gases created by combustion enter the heat exchanger. The heat exchanger is made up of a series of pipes, which the hot gas travels through. Surrounding these pipes is cold water. As the hot gas moves through the pipes, it heats the surrounding water that can then be used in your heating system or supplied to your hot taps.
4: Byproducts exit the system
The only byproduct of burning hydrogen and oxygen is water and nitric oxide, and so a condensate is required for this water to escape the system. The hot flue gases (hydrogen and oxygen) can also exit the system via the flue along with some NOx emissions as a result of hydrogen combustion.
The hydrogen boiler continues to pull in more hydrogen and oxygen so that this whole process can be repeated again and again.
Where do you store the hydrogen for house boilers?
When hydrogen-ready boilers become available, there will be no need for in-home storage, such as a tank, for the hydrogen. The hydrogen instead will be added to the UK’s gas supply and will therefore automatically be burned by your boiler.
Will gas boilers be replaced by hydrogen?
With the government’s ban on gas boilers in new build properties from 2025, heat pumps and hydrogen boilers could be the way forward. But currently, there isn’t an approved boiler that can use 100% hydrogen.
Two show homes have been built in Gateshead, London that contain gas appliances fully powered by hydrogen. These appliances include hobs, fires, boilers and even a barbecue. The houses are available to look around and were partially built for the purpose of education. They demonstrate how hydrogen could be used in the future to create greener homes, but unfortunately, we aren’t there yet.
