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• Methods of home heating Homes and businesses around the world are mainly heated by coal and natural gas. To reduce greenhouse gas emissions, these fuels could be replaced by electricity, low-carbon gas (such as hydrogen) or heat networks
• Hydrogen in the gas network We can potentially use existing gas pipes to carry hydrogen for heating homes and businesses
• Using hydrogen safely in the home Heating and cooking appliances would need to be adapted or replaced, and there are cost and safety considerations
• Case studies in the UK The UK is leading the way in hydrogen heating projects

Whether it is for warming a room, cooking a meal, or taking a shower, heating in homes requires a lot of energy. Producing heat without using fossil fuelsMaterials containing carbon, formed long ago by geological processes acting on the remains of living organisms. Examples include coal and natural gas is a big challenge – in 2017, 23% of all the energy consumed globally was used for space heating, water heating and cooking, and only 10% of this was produced from renewable sources. There are a number of low-carbon heating methods we could use instead, which include burning hydrogen.

Methods of home heating

Global heat generation is dominated by coal and natural gas, which are relatively cheap and abundant. When they burn, they produce harmful emissions such as carbon dioxide (CO2) and nitrogen oxidesA group of nitrogen gases that contribute to air pollution, smog, acid rain and climate change (NOx) which contribute to air pollution and climate change. Three sustainable heating methods we could use instead of fossils fuels are:

1. Low-carbon electricity, used to power storage heaters and heat pumpsA device that transfers heat from one area to another, often using electricity
2. Heat networksA system that supplies heat via insulated pipes to homes and businesses from a central source (also called district heating) – a series of pipes deliver heat to homes from a central, low-carbon energy sour
3. ‘Green’ gases – hydrogen, synthetic natural gas or biogasA gas mix produced when organic matter breaks down without the presence of oxygen, mainly consists of methane and carbon dioxide

Replacing fossil fuels for heating is an enormous task, and it is likely that all three of these options will be required in some form. This guide explores the potential of the ‘green’ gas option, and how hydrogen could contribute to sustainable, low-carbon home heating.

Hydrogen in the gas network

Some countries such as the Netherlands and the UK already have a national network of natural gas pipes linked up to most homes and businesses. People in these countries are used to using natural gas for heating and cooking, and hydrogen could act as a low-carbon replacement. Just like natural gas, hydrogen can be transported through pipes and burned in the home using a boiler or stove; the only waste products at the point of use are water and some NO_x gases.

20% hydrogen

Mixing some hydrogen into the natural gas we use today could reduce greenhouse gas emissions without disrupting homeowners and businesses. For example, a gas mix that is a blend of 20% hydrogen and 80% natural gas by volume can be used in an existing natural gas network without changing any pipes or appliances – this enables a small CO₂ saving (about 6%) compared with just using natural gas. An example of this is the HyDeploy project at Keele University in the UK. A second phase of the project will see Northern Gas Networks supplying around 650 homes and businesses in the north east of England with a hydrogen and natural gas blend.

100% hydrogen

Converting a natural gas network to use 100% low-carbon hydrogen could save significantly more CO₂, but it is a bigger logistical challenge. While it would be unusual, switching over to a new type of gas is not unprecedented; during the mid-20th century in the UK, USA and Australia, many homes switched from using so-called town gasA manufactured gas that is mainly a mix of hydrogen and carbon monoxide, can be used for heating and cooking to natural gas. The UK switch-over took 10 years to complete and required the replacement or modification of over 40 million household gas appliances.

Gas networks have two main parts – the transmission system, which is like a motorway that moves gas long distances at high pressure, and the distribution system, which is like a series of smaller roads moving gas into homes and offices at lower pressure.

The distribution system can be adapted to use hydrogen instead of natural gas. Homes and offices would need to modify or replace their gas appliances, but infrastructure would essentially remain the same. Old gas pipes, valves and joints need to be checked for wear and tear, as hydrogen leaks easily from small gaps. In the UK, new plastic (polyethylene) pipes are being installed to replace older iron and steel versions, and these new pipes can safely carry hydrogen at low pressures, with little risk of leakage.

It has been argued that converting a natural gas network to carry hydrogen would save money compared to other forms of low-carbon heat, due to it minimising disruption and reducing the amount of new, expensive infrastructure needed. For instance, the H21 suite of gas industry projects aims to provide evidence in support of re-purposing the UK gas network. However, existing pipelines would still need some investment and the transmission system would need to be modified or replaced. Transmission systems use steel pipes to carry natural gas at high pressures (up to 75 barA metric unit of pressure, 1 bar is roughly equal to air pressure at sea level in the UK), and steel can be damaged by high-pressure hydrogen, becoming weak and brittle.

Using hydrogen safely in the home

If natural gas is replaced with 100% hydrogen, heating and cooking appliances will need to be adapted or replaced. This is because hydrogen has different properties from natural gas – for example, it burns at a higher temperature. Companies such as Worcester Bosch, Giacomini and BDR Thermea (BAXI) are already developing hydrogen-ready appliances for use in homes. These appliances would work normally with natural gas, but could also be used with hydrogen if the gas supply switched over. An Australian company (Heatlie) has even developed a hydrogen-fuelled barbecue. Research projects such as Hy4Heat and HyHouse are testing to make sure these new appliances are safe and easy to use.

Boilers

Natural gas boilers have a part called a flame failure device, which uses sensors to stop gas from flowing if the flame goes out. The sensors used in natural gas boilers do not work with hydrogen, but engineers are working on new versions that do, using infra-red or ultra-violet light. To make sure hydrogen boilers are safe, these devices need to be fast acting and reliable.

Fireplaces

Hydrogen burns with a very pale blue flame which is almost invisible to the naked eye. Adding a chemical called a colourant to the flame would make it easier to see, which is safer and more aesthetically pleasing. Work is ongoing to find a suitable colourant that is cheap, non-toxic and compatible with hydrogen. An alternative option would be to design a heating element that glows when in use.

Cookers and ovens

Hydrogen cookers would require a re-designed burner, in order to manage the higher temperatures hydrogen burns at and to limit the release of harmful NOx gases. This may include reducing the size of the burner holes, using new materials, or other methods of limiting oxygen concentration at the point of ignition. Using hydrogen is not expected to impact on cooking performance or require new kitchen utensils.

UK hydrogen for heating pilot projects

There are a number of studies and projects in the UK testing out whether replacing natural gas with hydrogen is safe, how much it would cost, and how disruptive the process would be.