Key Differences: Air vs Ground Source Heat Pumps
If you are considering making the switch to a renewable heating system, you are not alone. Thousands of UK homeowners are leaving behind traditional gas boilers and embracing sustainable heat pump technology. There are two key options available on the market: air source heat pumps and ground source heat pumps.
The good news is that whatever your situation is, there is likely to be a heat pump solution out there which will suit your needs and budget. And with government grants like the full funding under the ECO4 scheme and Boiler Upgrade Scheme, offering up to £7,500, the financial barriers have never been lower.
Within this blog, we’ll break down everything you need to know about ASHPs and GSHPs, including how they work, their efficiency in UK climates, what installation entails, how much they cost, their maintenance, and most importantly, which would be right for your home.
An air-source heat pump doesn’t generate heat, it moves it, working much like a refrigerator in reverse. An outdoor unit houses a fan that draws in air, even when it’s freezing outside.
This air then passes over a network of refrigerant-filled coils. The refrigerant, which has a low boiling point, absorbs thermal energy from the air and evaporates into a low-pressure gas. This gas then travels to a compressor, which puts the gas under intense pressure, greatly raising its temperature. This now-hot gas circulates through an indoor heat exchanger, passing its warmth onto your home’s heating system, either radiators or an under-floor heating loop.
After cooling, refrigerant passes through the expansion valve to decrease in pressure and temperature before it returns to the outdoor unit for another cycle. This process runs continuously; thus, heat energy is transferred from outside to inside.
Efficiency in this process is measured by something called the Coefficient of Performance, or COP. A COP of 3 means that for every unit of electricity the system consumes, it produces three units of heat. Modern air source heat pumps consistently achieve COPs in the range of 3 to 4.5, making them far more efficient than burning fossil fuels.
Ground source heat pumps operate on the same thermodynamic principles as air source systems, but they use a source, the earth.
Whereas air source heat pumps rely on the outdoor air, making it dependent on the weather, ground source systems make use of the natural phenomenon where the ground temperature remains fairly constant throughout the year, within a temperature of 8°C to 12°C even in the coldest parts of the UK.
This is done through a network of pipes buried underground, either horizontally through trenches or vertically through boreholes. It circulates a mixture of water and antifreeze that absorbs low-grade heat from the surrounding soil. The warmed fluid rises back above ground to the heat pump unit, where the thermodynamic process takes place. In this way, the thermal energy is absorbed by the refrigerant inside the heat pump, gets compressed, and transfers the concentrated heat to your home’s central heating system.
Most of the installations in the UK are closed-loop systems, a sealed circuit in which the water/antifreeze mixture circulates. Open-loop systems, where the groundwater is extracted directly, may be used in properties with access to good clean water sources, but these are less common and careful environmental assessment is required.
The advantages of closed-loop systems is that they are contained, sustainable, and do not deplete water resources. They are also the standard recommended approach by environmental regulators.
A well known myth is that air source heat pumps stop working efficiently in cold weather. The reality is that modern ASHPs perform incredibly well, even in the harshest of UK winters.
Cold-climate versions can maintain a COP of more than 3.0 even when outdoor temperatures drop down to -15°C, colder than most UK winters ever get.
ASHPs in Scotland proved that ASHPs maintained a COP of around 2.8 during winter months, delivering consistent 25% savings on heating costs compared to the previous gas boiler systems. The important difference from gas boilers is that heat pumps run more continuously at lower capacity rather than in short bursts, meaning your home stays at a steadier, more comfortable temperature without much fluctuations.
Overall, when looking at real-world impact, GSHPs are usually 10–25% more efficient than ASHPs when assessing over a whole heating season. In practical terms, this may mean an extra £200–£400 annual saving, depending on the size of your property and your heating needs.
For most UK properties, especially in southern England and the Midlands where winters are relatively mild, the difference in efficiencies between a well-installed ASHP and GSHP is modest. The real comparison becomes one of cost versus efficiency. In the most northerly regions and on properties in genuinely cold microclimates, the gains in efficiency from GSHP could become substantial.
Installation differences between these two systems are quite dramatic, and is often where the decision becomes clearer for many homeowners.
Installing an ASHP is relatively easy. The main outdoor unit, about the size of a large air conditioning box, simply needs an outdoor space with good ventilation. A location might easily be against a garden wall, on a flat roof, or in a courtyard. Some installations even take place on a balcony, following new permitted development rules from May 2025.
Installation normally takes 3–5 days with minimal disruption to your property or garden. Indoor components are usually compact, fitting neatly into an existing airing cupboard or utility room.
In addition, ASHPs are suitable for installation in most UK properties, including many urban homes with terraces and smaller gardens.
Installation of GSHPs is another matter altogether. There is an intensive groundworks phase:
Requires digging trenches 1-2 metres deep across your garden—typically needing 100–200 square metres of ground space depending on your property’s heating requirements. Trenches might be 100 metres long, snaking across multiple sections of garden.
This involves very deep drilling into the ground, perhaps 100 metres or more per borehole, to create vertical heat exchange paths. Not as invasive to one’s garden, but much more expensive due to the specialist drilling equipment.
Installation generally takes 2–4 weeks but causes considerable temporary disruption, as your garden becomes similar to a building site, complete with heavy machinery, excavation, and extensive ground disturbance. The disruption is temporary, and land can be wholly restored afterward.
GSHPs work best for properties with significant garden spaces.
For urban terraces, semi-detached homes, or properties with limited outdoor space, GSHPs often simply are not practical.
In hybrid systems, there is a combination of a gas boiler and an air-to-water heat pump with smart controls that automatically switch between the two units, based on demand and outside temperature. The heat pump can operate independently in good conditions, when the weather is milder, say. The gas boiler provides additional heating when there is extreme cold or high demand.
They generally cost in the range of £7,500 to £11,000. Note, though, that hybrid systems are not covered under the Boiler Upgrade Scheme.
For many homeowners, the upfront cost is usually the deciding factor, so let’s break it down completely.
| Property Type | Installation Cost | After ECO4 grant | After £7,500 BUS Grant | Typical Heat Pump Size |
|---|---|---|---|---|
|
1–2 bedroom flat/terrace
|
£7,000–£9,000
|
£0
|
£0–£1,500
|
4-6kW
|
|
3 bedroom semi-detached
|
£8,000–£11,000
|
£0
|
£500–£3,500
|
6-8kW
|
|
4+ bedroom detached
|
£10,000–£13,000
|
£0
|
£2,500–£5,500
|
8-16kW
|
£2,000–£5,000 (not always necessary; depends on your existing system)
Underfloor heating installation: £5,000–£15,000 Improvements to insulation: £1,000-£5,000 (often worthwhile to maximise efficiency)
if eligible under the ECO4 scheme, additional upgrades like bigger radiators and insulation are fitted for free. Fill in our simple 1 minute form and transform your home and lower your energy bill today!
| System Type | Installation Cost | After ECO4 Grant | After £7,500 BUS Grant |
|---|---|---|---|
|
Horizontal ground loop
|
£20,000–£30,000
|
£0
|
£12,500–£22,500
|
|
Vertical borehole
|
£25,000–£40,000+
|
£0
|
£17,500–£32,500+
|
GSHP systems are much more costly, about 2-3 times the cost of ASHPs. The largest contributor to their cost is ground preparation, which can include horizontal trenching and pipework, or vertical drilling, which is a highly specialist task and is expensive to carry out.
The important fact is that, though considerably more expensive to install, GSHPs occasionally qualify for additional government support under schemes such as ECO4, provided one’s household meets certain criteria, which will allow the system to be installed without any cost to you.
| Home Type | Annual Gas Boiler Costs | ASHP Annual Cost (COP 3) | GSHP Annual Cost (COP 3.5) |
|---|---|---|---|
|
2-bed terrace
|
£720
|
£660
|
£570
|
|
3-bed semi- detached
|
£1,080
|
£990
|
£857
|
|
4+ bedroom detached
|
£1,440
|
£1,320
|
£1,140
|
The shift from fossil fuel heating to renewable heat pumps represents more than just a financial decision; it’s an investment in your home’s future, your comfort, and the environment.
Whether you choose an air source heat pump for its accessibility and cost-effectiveness or a ground source heat pump for its superior efficiency and reliability, you’re making a choice that positions your home for the sustainable future toward which the UK is moving.
The financial case is persuasive: upfront barriers are radically reduced by available government grants, and long-term energy savings often exceed £500–£1,000 per year.
Heat pump technology has developed dramatically, and modern systems perform reliably even in UK winters, dispelling reasons that have deterred adoption thus far. The only decision remaining is whether now is the right time for you, and increasingly, for most UK homeowners, the answer is yes.
Don’t face this decision on your own. Our team at Warmer Home Grant brings together technical knowledge with a real commitment to helping UK homeowners get the heating they deserve for free or at a very low price.
Check your eligibility for government grants today by simply filling in our quick online form, and we’ll provide personalized guidance on which system suits your home, how much you could save, and what government support you qualify for.
There’s no obligation, just straightforward advice from experts who have helped thousands of UK families make this transition. Your warmer, greener, more affordable home is waiting. Let’s get you there.
Warmer Home Grant is one of the major energy grant suppliers committed to supporting UK homeowners in their drive for renewable heating solutions through government support schemes.
We specialise in air source and ground source heat pump installations that lead the way in affordable, quality, and environmentally responsible solutions.
With our team of Gas-Safe registered installers and grant specialists, we make transitioning to sustainable heating as easy and hassle-free as it could be. Ready to explore heat pumps? Fill in our 1-minute form or contact us now!
At Warmer Home Grant, we specialise in helping UK homeowners get the highest amount of funding they are entitled to under government-backed schemes aimed at reducing their bills and carbon emissions.
We understand that trying to navigate through heat pump grants, eligibility requirements, and selection of installers can be daunting, and that’s why we have streamlined the process: taking care of the whole application process and providing support whenever you need it! We will always assess your property and circumstances against the latest grant criteria along with all other funding availability. These efforts helps ensure that you gain access to all funding and upgrades that you may qualify for.
From our friendly team of advisors to professional Gas-safe registered installers, you know you are always in safe hands. If you have any enquiries, please don’t hesitate to contact us. The ECO4 scheme only runs until March 2026 and is a limited funding opportunity. Act now by completing our simple 1-minute eligibility form and secure your new system for free!
| Area Covered | Area Covered | Grant Amount | ASHP Installation Savings | Relevant Info |
|---|---|---|---|---|
|
Boiler Upgrade Scheme (BUS)
|
England, Wales
|
£7,500 off installation costs
|
can reduce installation cost to as low as 500.
|
Must replace fossil fuel heating, valid EPC
|
|
ECO4 Scheme
|
UK
|
100% of ASHP cost
|
Full cost for eligible households
|
Based on household income, benefits and fuel poverty
|
|
Nest Scheme
|
Wales
|
Coverage up to full cost for eligible
|
Potential to reduce bills by up to £800/year
|
For low-income or fuel poor households
|
|
Warmer Homes Scotland
|
Scotland |
Up to £7,500. £9,000 for rural.
|
Annual heating savings of £500–£950
|
Additional support for rural areas, loan options
|
|
Home Energy Scotland (HES)
|
Scotland |
Up to £7,500 grant, or £9,000 for rural, and up to £15,000 interest-free loan
|
Annual savings up to £950
|
Both grant and loan available for eligible households
|
|
0% VAT Incentive
|
UK-wide
|
0% VAT on ASHPs until March 2027
|
average 5% savings on upfront cost
|
Applied automatically
|
