Gas Boilers Vs. Ground Source Heat Pumps

Around 85% of UK homes use gas-fired central heating.¹ To reduce carbon emissions, combat air pollution and help stop climate change, there must be a radical shift in how we heat our buildings.

But why are ground source heat pumps better than gas boilers? And how does the lesser-known heat pump compare to the oh-so-familiar boiler? We look at the two technologies and how they compete in efficiency, cost, carbon emissions and more.

Gas boiler vs ground source heat pump

The future of gas vs. ground source heating

Why are gas boilers being phased out?

To achieve the UK’s legally binding target of net-zero carbon emissions by 2050, it’s vital that fossil fuels, including natural gas, are phased out and replaced with renewable alternatives.

A big benefit of a ground source heat pump is that it future-proofs properties – both in terms of sustainability and conforming to regulation. From 2025, the government has confirmed that gas boilers will no longer be an option for new builds. They are even set to commit to cutting carbon emissions by 78% by 2035, meaning that a significant amount of gas boilers will have to be ripped and replaced. In fact, to tackle the climate crisis, it’s possible that by the mid-2030s, the installation of new gas boilers will be banned entirely.

It’s not just the low-carbon reasons. Renewable heating systems, such as ground source heating, come without the flammability, risks, flues and regulations associated with gas. Using a non-flammable refrigerant, heat pumps such as the Shoebox also avoid the risks, servicing and expenses of fossil fuel systems.

The early bird catches the worm!

Sooner or later we are all going to have to reconsider how we heat our homes, so we’re encouraging anyone with the opportunity and budget to invest in ground source heating to do so sooner. This is because there are funding streams available right now – such as the Domestic Renewable Heat Incentive, which offers the most generous payback there will ever be for a single home project.

It’s safe to say that the majority of households are familiar with gas boilers. But with all of these vital targets considered, something is going to have to take the commonplace position of the gas boiler for most of our homes –  this is where heat pumps come in!

How they work

Gas boiler

A gas boiler heats water by pumping it into pipework over a series of gas flames. Just like liquid in a pan, the water is heated up as it passes the flames. It is then used to deliver central heating and hot water to the home. There are different types of boilers, such as combi boilers, which give you instant hot water – meaning you don’t need a hot water tank.

As gas is a fossil fuel, it releases carbon dioxide (CO2) – a greenhouse gas that contributes to climate change. The combustion of fossil fuels also releases particulates, NOx and SOx into the atmosphere that contribute to global warming and air pollution.

Ground source heat pump

A ground source heat pump is an electrically-powered heating system. Using buried pipework filled with a heat transfer fluid (usually glycol), the system absorbs low-grade heat energy from a renewable energy source, such as the ground or water. The heat pump then compresses this heat energy to raise its temperature.

Heat exchangers transfer the additional heat energy from the glycol fluid to the water piped through the home’s heating distribution system, upgrading this to a higher temperature. The newly heated hot water can be used for space heating delivered by radiators or underfloor heating, and also for domestic hot water stored within a cylinder.

The underground pipework, known as a ground array, can be installed on an individual or communal level – providing a sustainable and naturally replenished source of heat for either a single home or a whole street. Kensa has pioneered an infrastructure that mimics the existing gas network, facilitating the installation of ground source heat pumps on a larger scale. This is known as a Shared Ground Loop Array.

Carbon emissions & environmental impact

Gas boiler

Some 37% of the UK’s carbon emissions come from demand for heat (of which 17% is space heating and 4% is hot water), which is mostly met by burning natural gas. In fact, the typical emissions from a gas boiler are 226g/kWh which add up to 2.7 tonnes per year for an average house. This level of emissions equates to travelling 12,000 miles in an average family car – that’s enough to get you from London to Auckland (11,386) with miles to spare.²

Not only that, but fossil fuel heating systems contribute to air pollution. This comes in three main forms: particulates, Nitrogen Oxides (NOx) and Sulphur Oxides (SOx). These are pollutants that contaminate the air, posing a significant threat to the planet and public health.

As more people realise that gas-fired systems are incompatible with a net-zero carbon world, there must be a radical shift in how we heat our buildings if the UK is to reach its environmental goals.

Ground source heat pump

Ground source heating is certainly the winner when it comes to reducing carbon emissions. By its very nature, the system is sustainable, as the ground or water from which the heat energy is extracted are renewable heat sources. Ground source heating uses some electricity which creates some emissions but the emission levels of a ground source heat pump is just 53g/kWh, delivering a whopping 77% saving on emissions versus gas.³ It’s certainly a sustainable alternative to short-term ‘sticky plaster’ solutions to heating homes, such as hybrid systems.

One of the main reasons the emissions are so low is due to the heat pump’s extremely high efficiency – delivering around three to four units of renewable energy for every one unit of electricity.

And it gets even better. As the electrical grid continues to rapidly decarbonise due to generation from renewable sources such as wind and solar farms, so does that small amount of electricity consumed by the ground source heat pump – meaning the heat pump you install today will emit fewer carbon emissions in the future. Ground source heat pumps are also compatible with renewable technologies such as solar PV – like in this case study, which utilises solar energy and converts it into electricity – the use of which can further improve a property’s sustainability.

We will reduce emissions through shifting from gas to electricity to heat our homes and by better insulating the buildings in which we live and work.

The Energy White Paper, Powering our Net Zero Future

Efficiency & performance

Gas boiler

Modern condensing gas boilers can be around 90% efficient. This means that 90% of the energy used by the boiler goes to heating the home, while the remaining 10% is waste heat that is passed through the flue to the outside. The heating system isn’t as efficient as it could be because of this wasted heat.

Not even home improvements would make a huge difference to the system’s efficiency. The only real benefit of adding energy efficiency measures, such as insulating the property, is that you’re using fewer kilowatt-hours (kWh) of energy per year. On the other hand, energy efficiency measures coupled with a heat pump give you a double win; you can actually go back and improve insulation to improve the efficiency of the system.

Ground source heat pump

Ground source heat pumps can be 300 – 400% efficient, which means they can deliver three to four times the amount of energy they consume from electricity. When multiple properties are linked to a shared ground array system, there is even a chance to increase this performance by utilising waste heat from applications such as server rooms and supermarkets – the options are endless.

When comparing ground source heating to gas, it’s important to consider the relationship between flow temperature and efficiency. A ground source heat pump operates at a lower flow temperature than a boiler, but that’s certainly not to say the heat pump doesn’t reach the building’s required temperature; it may just require a larger surface area such as underfloor heating or a larger radiator.

For example, a room that needs 500W can be heated just as quickly by a larger radiator operating at 50°C as by a small radiator operating at 70°C. The lower the temperature is, the higher the efficiency of the system.

Funding streams & models

Available for ground source only

Government funding streams incentivise the adoption of renewable technology such as ground source heat pumps. It is in the UK’s best interest to make these technologies approachable and affordable, as they will help achieve net-zero carbon emissions by 2050.

At present, heat pump projects featuring an individual home have access to a big incentive: the Domestic RHI. On average, this can provide a homeowner with a typical income of £26,000 over seven years.

Meanwhile, in projects involving heating multiple buildings – such as heating homes across an entire street – the economy of scale and technology efficiency increases. For households who don’t currently have the budget to install ground source, we believe district heating with heat pumps is the key to decarbonising heat while making the technology affordable. Funding mechanisms will make this possible, such as split ownership, where the ground array – the most expensive part of any ground source heat pump installation – can be funded by a separate entity.

DISCOVER FUNDING OPTIONS

Upfront cost

Gas

The upfront cost of a gas boiler installation is much cheaper than a ground source heat pump. This is to do with the fact that around 1.6 million gas boilers are installed each year, compared to around 30,000 heat pumps. You may expect to pay out between £1,500-£2,500 for a boiler.

While the upfront installation and running costs of a gas boiler may seem appealing, it’s important to think about the impact fossil fuel heating has on the environment and the way homes will be heated in the not-too-distant future. In fact, this report recommends that the government changes the environmental levies on the electricity bill into a carbon levy on electricity, gas and oil bills, based on their carbon impacts. If implemented, this could see gas bills rise substantially.

Ground source

Like many renewable heating technologies, installing a ground source heat pump requires a capital outlay that is significantly higher than a gas boiler. At the moment, the upfront cost of the entire system, including ground arrays, can start at anything from £10,000 – £15,000. In spite of the higher upfront cost, we have seen thousands of homes and businesses across the UK opt for a heat pump because they want to significantly reduce their carbon footprint, lower their long-term running costs, and future-proof their properties.

As deployment volumes increase in line with government ambitions to install 600,000 heat pumps per year by 2028, we expect to see significant drops in prices for heat pumps and the provision of the ground array. It’s unlikely that heat pumps will ever quite reach gas boiler prices because they contain more raw material – metal in the form of compressors and larger heat exchangers – but the gap will close. Government funding streams, such as the RHI, play an important role in reducing costs and providing payback for those installing renewable heating systems.

Running & replacement costs

Gas

Gas heating has been long recognised as a cheap source of heat although the running cost of gas fluctuates with many factors, such as market reforms or world events that affect the availability of gas – pushing prices up or down. For example, as of December 2020, prices fell in the 12 months previous, which meant the fuel is currently very low cost – but this changes frequently.

Ground source

Ground source heat pumps compare favourably with gas and were very similar until very recent gas price drops. However we expect the running costs of ground source heating to further drop with the adoption of smart methods such as load shifting. This means, using smart controls and time-of-use tariffs, the ground source heat pump can automatically run when electricity is low in cost and carbon. This is usually in line with periods of renewable electricity production from sources such as wind and solar.

Load shifting means you can avoid expensive times, and even take advantage of the fabric of the building. For example, if you like to have your heating on at 20ºC by 5 pm, most heating systems would turn on at 4.30 pm and gradually bring your house up to temperature for, say, when you get home from work. However, if this system looks ahead at energy prices and realises it will be expensive between 4.30 – 6.30 pm, it might turn the heating on at 2 pm – bringing the temperature up to 22ºC and cooling down to the perfect 20ºC when you return.

Smart controls learn your heating preferences and devise a customised heating schedule for your home that provides optimum comfort, whilst saving you money. Heat pump projects such as Energy Superhub Oxford estimate that this could deliver savings of up to 25% compared to a standard ground source heating system. On average, this means that ground source heating can be cheaper than gas. A win for the environment and for our pockets.

The savings can increase even further when using physical energy storage such as a heat battery, which means you can store the heat following consumption at off-peak times, and use it when required.

As for lifetime costs, an average boiler will need replacing every 10 to 15 years, whereas ground source heat pumps will typically last 25 years and do not require annual servicing – saving you even more. The ground array pipework used to extract the heat energy will last for 100 years, so installing this infrastructure is a one-off investment to provide heat for generations. Lastly, if you disconnect the property from gas completely, you save yourself the gas standing charge.

Anyone who can install a gas boiler can install a heat pump

Darren Veal, Kensa's Technical Support & Commissioning Manager

Installation

Unlike a gas boiler system, a ground source heat pump has no flue or ventilation requirements, no condense pipe to fit, no more landlord gas safety checks, and simple and clean servicing.

But just like a gas boiler, a ground source heat pump can be installed inside the home. The ultra-small and quiet Shoebox heat pump is designed especially for flats, apartments or homes where saving space is a priority. The extremely efficient Evo heat pump is a stylish and peaceful match for modern homes.

The groundwork part of the installation is completed outside – minimising disruption to the home, and once the ground has been restored, they are visually unobtrusive. Other than the ground element, the installation of a heat pump is not too dissimilar from a gas boiler; it’s a simple process for any competent plumber. We see the ground array infrastructure as an imitation of the gas network; in the same way an installer wouldn’t design the gas infrastructure, they do not need to design the ground array – this element is left to Kensa.

We have a UK-wide network of experienced and trusted groundworkers and drillers who undertake the groundwork aspect of the project. We also provide technical support for the life of the system – both during and following the installation.

Controls & everyday use

Gas

An incomparable benefit of a gas boiler is that it’s a technology most of us are fairly familiar with – and that includes everyday use.

However, you may be surprised to learn that ground source heat pumps are just as simple to use, incorporating the easy controls that most households are already used to.

Ground source

A big benefit of ground source technology is its flexibility. A ground source heat pump system can be as smart or as simple to use as you like – integrating with your preferred controls and heating distribution system, such as underfloor heating or radiators, as well as other renewable technologies.

A heat pump is designed to be a ‘fit and forget’ technology. In fact, you can adopt the same controls that you would have with a gas boiler, designed to provide maximum comfort with minimal servicing requirements.

Mass adoption

Gas

For the majority of households connected to the gas grid, a gas boiler is a trusted technology. However, the way we heat our homes has to change; we are already seeing the devastating effects of climate change – this is the decade to make a difference and create a sustainable future. If we are to achieve the target of net-zero emissions –  by offsetting carbon emissions – the UK must adopt another tried-and-tested, but renewable, technology.

Ground source

Switching domestic properties to non-combustion heating systems would significantly reduce these harmful emissions and move the UK closer to its net-zero target. According to the Climate Change Committee, electrification of heating is the most effective route for reducing carbon in housing.

Kensa sees a future where the ground array infrastructure imitates the gas grid and facilitates the mass installation of ground source heat pumps. Deployed on a street-by-street basis, the adoption of this 21st-century network would mean that households can simply ‘connect’ their heat pump to the network. The only cost to the household would be the unit itself, as the ground array can be funded by a separate entity that benefits from a modest ‘standing charge’, similar to when connecting to the gas grid.

The 2020s must be the decisive decade of progress and action.

Climate Change Committee, The Sixth Carbon Budget (The UK's path to Net Zero)

Case studies: ground source vs. gas

Eco house in East London

Architect, Jason, designed and built his very own ultra-modern, eco-friendly home. He wanted his green haven in the city to be as self-sufficient as possible and was keen to install a renewable heating system rather than using the gas network. Cue the Kensa ground source heat pump.

See the case study

Ground Source Review Wanstead, Eco House Heat Pump 7

Together Housing tower blocks in Blackburn

Housing association, Together Housing, wanted to replace old gas boilers across three tower blocks. Motivated to invest in environmentally friendly and affordable heating systems for their residents, they decided ground source heat pumps were the best option – specifically the Kensa Shoebox.

The ongoing scheme, supported by Kensa Contracting, already demonstrates the benefits of replacing gas with ground source on a large scale; it will maintain the residents’ comfort and safety, while making huge savings on carbon emissions.

See the case study

Grade II listed farmhouse in Cambridge

One of the biggest myths about ground source heating is that it can only be installed in new-build homes. This certainly wasn’t the case for this listed home.

When Keith and his family moved to a spacious farmhouse in Cambridge, the 20-year-old gas boiler had to move out. The heating was pricey and the temperatures weren’t up to scratch. Eager to step away from fossil fuel reliance, Keith opted for ground source heating.

See the case study

Ground Source Review River House ǀ Heat Pump - Keith Clarke in front of River House

We realised that we could get the whole thing paid for with the Renewable Heat Incentive, including the installation. Plus, we’ve ended up with a system where the yearly cost of electricity is less than we would have been paying for gas.

Keith - homeowner

References

1. The Guardian, 2020
2. Based on 12,000 kWh of heat. Gas boiler carbon intensity calculated using SAP figure, which has been divided by typical gas boiler efficiency.
3. This article quotes an average carbon intensity of 181 g/kWh for electricity, which has been divided by typical heat pump efficiency of 3.5. Gas boiler carbon intensity calculated using SAP figure, which has been divided by typical gas boiler efficiency.