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Decarbonisation of home heating: calling time out


6 min read

Cartoon of a hydrogen molecule in the form of a blue teardrop shape wearing boxing gloves in a boxing ring and fighting a green heat pump Cartoon: Brian Davis
The fraught debate on the pros and cons of hydrogen boilers versus heat pumps needs to be more informed

Cartoon: Brian Davis

The debate on the decarbonisation of home heat has been gaining intensity. Oversimplified to a fight between heat pumps and hydrogen, the discourse on social media platforms is getting fraught, writes Nick Wayth, CEO of the Energy Institute.

However, it’s an important debate that we all need to understand if we’re to make informed choices that benefit our homes, our national energy demand and the path to net zero. Rather than add another voice to the online melee, we need to find space for informed debate and not get stuck in the competitive advocacy of one camp or another. This debate must lead to further understanding and greater participation by those that are making choices – government, regulators, consumers, housebuilders and landlords.


Why is this an important issue today?  
Domestic heating accounts for around one-sixth of the UK’s CO2 emissions. The UK, where 80% of UK homes are heated by natural gas, has announced bans on gas boilers in newbuild homes from 2025 and for all new boilers by 2035. Decarbonising 28mn homes whilst balancing supply and demand on the coldest, calmest winter nights is a monumental task but one that we must tackle.  


We are going to have to make choices in the years ahead, and, for many, it’s just too polarised and confusing to know what realistic options are.


As a chartered professional body, it is not the Energy Institute’s role to lobby or advocate for one technology over another. Nevertheless, it is our job to provide science-based expertise and facts to help inform energy decision-making. Here, I hope to explain the principal technologies available today and the wider issues impacting the UK heating sector for the benefit of policymakers and consumers as well as our sector.


So, what are the options?  


Air-source heat pumps
Most experts argue that air-source heat pumps are likely to be the dominant solution. They work like a fridge in reverse, compressing air from the outside to heat it and then transferring it into a conventional hot water central heating system. Their key advantage is efficiency – one unit of electrical energy transfers into up to four units of heat energy. This is not magic, it is the first law of thermodynamics in action. Even if it’s cold outside, the air contains heat energy which is increased through mechanical work.


One less-known strength of heat pumps is that some can be run in reverse to provide cooling, something that will be increasingly important if the trend of hotter summers due to climate change continues.


A common counter argument is that heat pumps only work in very well-insulated homes. A 2021 report by the Energy Systems Catapult debunked this as a myth. Research based on 742 homes concluded that ‘no identified particular type or age of property cannot have a successful heat pump installation’. Although a heat pump will work most efficiently if a home’s insulation is improved.


However, the additional electrical demand, alongside electric vehicle (EV) penetration, will require reinforcement to electrical transmission and distribution. It should be noted that much of this investment will be required for EVs anyway. We will also need to see huge increases in low carbon generation to ensure that CO2 emissions are minimised. Smart technologies, using time-of-use pricing, will play an important role in balancing the supply and demand of power and grid constraints.


The other obstacles for heat pumps to overcome are installation costs, and the modifications to piping and radiators that some homes will require. As [heat pump] supply chains grow, heat pump costs are expected to decline and improvements in insulation will lessen the need for home modifications.


Hydrogen boilers – pros and cons
Advocates for hydrogen boilers argue that they offer consumers a ‘plug and play’ replacement for natural gas boilers. Hydrogen boilers are expected to cost no more than natural gas boilers, and heating would work in much the same way. Hydrogen is expected to be supplied from renewable sources (as green hydrogen) or from decarbonised CCUS (carbon capture, use and storage) natural gas (blue hydrogen).


However, an increasing body of scientists and engineers are challenging the role of hydrogen for domestic heating. A recent evidence review by Jan Rosenow of Oxford University found that none of 32 independent studies supported the role of hydrogen in domestic heating.


The main argument against hydrogen for heating is the operating cost. Up to six times more renewables, via green hydrogen, will be required for the same heat output as a heat pump using green hydrogen. Meanwhile, blue hydrogen will be subject to the volatility of international gas prices and the additional cost of delivering CCUS.


A recent report from the Royal Academy of Engineering’s National Engineering Policy Centre (which the Energy Institute supported), highlighted that using hydrogen for domestic heating could divert low carbon hydrogen from other use cases where there is no alternative – paradoxically slowing, rather than accelerating, the energy transition.


Switching from natural gas to hydrogen would also require replumbing the gas network up to and into the home. Planned trials of hydrogen boilers will test consumer appetite, practical safety aspects (hydrogen has a much broader ignition concentration range than methane) and the impacts of NOx (nitrogen oxides) emissions (which, unless mitigated, are higher than methane due to the higher burn temperature).


Heat networks for decarbonisation
For high-density housing in towns and cities, close to industrial sites, heat networks offer another significant route to decarbonisation. The Association for Distributed Energy (ADE) highlights that around 450,000 homes are already connected to one of 14,000 heat networks today. This could increase to 8mn customers (including commercial customers) by 2030, representing 17% of the UK’s heating needs.


One of the key advantages of heat networks is that the source of energy can switch to better and lower carbon options through time, without impacting end-consumers. The key challenge is that heat networks require whole communities to largely commit to a single source of heating.

Will some homes have no obvious low carbon solution today?  
Absolutely. However, these will make up only a small proportion of homes. Bioenergy, be that biomass, biofuel or bio-LPG (liquefied petroleum gas), are potential solutions. But let’s focus our efforts, for now, on the vast majority of homes where the solution is more obvious.


So how do we take this debate forward?


Is it as simple as betting on one of the above technologies? Unfortunately, not. There are several factors at play that impact how we should move forward. This means we need to approach heating our homes as an integrated system. Not as separate problems to be solved.


Energy efficiency
First, the cheapest, most reliable and lowest carbon form of heating is by addressing the heating we don’t use.


Tackling the energy efficiency of our homes should be treated as a national emergency. It will make a huge difference, regardless of what source of energy is used to heat our homes.


Well-insulated homes are warmer, healthier and cheaper to run. Government (both national and local) must step-in to help households, housebuilders and landlords address this issue – by providing clear policy, financial incentives (not complex grant schemes) and practical advice. Last week’s Autumn Statement provided welcome news, albeit long overdue, from the UK government.


The banking sector also has an important role to play, providing financial solutions to fund home efficiency investment, such as mortgage extensions and lower interest rates for energy efficient improvements – recognising that lower energy costs lower default rates.


Consumer information
Second, we need to help consumers understand their future heating options.


Of course, consumers should have choice. But those choices should be real, affordable and be presented in a transparent manner from trusted independent bodies, not businesses with vested interests. Assisted by these independent bodies, central and local government should start zoning the nation, region-by-region and ultimately street-by-street, to determine the predominant sources of heating.  


The options are unlikely to take the form of an à la carte menu.

Ideally, the planned 2026 timeline for the UK government to opine on the role of hydrogen and heating should be accelerated.


For most homeowners there may be only one or two credible options. Once consumers have greater certainty, they can start planning over a multi-year period.


If piping or radiators need to be resized, that can be done the next time home improvements are undertaken. Grid operators (both electricity and gas) can take a system view and plan for the investments they need to make. Whilst supply chains can start investing in manufacturing equipment and recruit the massive increase in the workforce that will be required.


Ideally, the planned 2026 timeline for the UK government to opine on the role of hydrogen and heating should be accelerated. This will give consumers greater certainty sooner.


Opening minds 
Finally, we need to recognise that we all have a lot still to learn.


Much of the learning will take place through doing – by undertaking trials, by early adopters investing ahead of others and in some instances, by error.


Nevertheless, we should recognise that no solution will be perfect, 100% of the time.


However, we do need to understand how a heat pump can keep a poorly insulated home warm when it’s –10°C outside. We need to understand the risks around transporting and handling hydrogen. We need to understand how consumers engage with largely unfamiliar heat networks. And we need to learn about the system implications of all these changes.


This debate is such an important one for the UK and for the future of clean, affordable and reliable heat for our homes. Let’s move the debate from simply social media and accelerate practical solutions, by developing coherent and unbiased plans that we can start putting into action.