Why Air Source Heat Pumps Trump Ground Source in the UK

The short version: air source offers similar performance for significantly less system cost and considerably easier installation, making it the technology of choice for most homes.

As the UK strives to decarbonize and transition towards renewable energy sources, homeowners are increasingly considering installing eco-friendly energy systems like heat pumps. For those who have heard of heat pumps, you may have also been left with the impression that ground source heat pumps are the ‘better’ option. Below, we explain why this is not the case for the vast majority of homes, and offer compelling reasons why air source heat pumps (ASHPs) are the best choice for most British households.

The difference in energy efficiency is marginal

One of the primary arguments for ground source heat pumps (GSHPs) is their higher energy efficiency, particularly during colder months. GSHPs absorb heat from the relatively stable ground temperatures, which can be advantageous when air temperatures plummet. However, in the UK's temperate climate, the efficiency gap between the two systems is often negligible.

Ground temperatures in the UK typically range from around 5°C at shallow depths to 10°C at depths of 6 meters. In contrast, air temperatures can fluctuate between -3°C and 17°C during the winter heating season. While this temperature differential may give GSHPs an edge on the coldest days, modern ASHPs can still achieve impressive efficiencies, with seasonal coefficients of performance (SCOP) ranging from 300-400%.

Air source is significantly more cost effective

While GSHPs may offer a slight edge in energy efficiency, their significantly higher upfront costs can quickly offset any potential savings on running costs. According to government data, the average ASHP installation cost is around £13,590 (excluding the Boiler Upgrade Scheme grant), while a GSHP installation averages a staggering £26,594 – nearly double the price. With such a substantial price difference, it would take well over a decade for the higher efficiency of a GSHP to offset the extra upfront cost through reduced energy bills.

Most homes don’t have space for ground source

GSHPs require extensive groundworks, including the installation of underground pipework (ground array) spanning hundreds of cubic meters across your garden. A general rule of thumb is to multiply your home's square footage by 2.5 to estimate the garden space needed - so a 100m² house may require around 250m² of trenching. This can be a significant undertaking, especially for those with limited outdoor space or living in densely populated areas. There are vertical ‘borehole’ options, but these require specialist drilling expertise and are generally not an option in urban areas or non-freehold properties.

Above: The two main types of ground array for GSHPs

In contrast, ASHPs are compact units, typically the size of a washing machine, that can be easily installed in most gardens or outdoor spaces. This flexibility makes ASHPs a more practical choice for the majority of homeowners who don’t have huge gardens (or don't want to dig them up!) or those living in urban areas with limited outdoor space.

Air source is significantly easier (and cheaper) to install

The installation process for GSHPs is often more complex and disruptive than that of ASHPs. A typical horizontal ground array installation involving trenching and pipework could take 5-7 days of groundwork alone. Vertical borehole systems, a specialist undertaking which may be needed for properties with very limited garden space, can involve 2 days of drilling per 60-100m deep borehole.

On the other hand, ASHP installations are relatively straightforward, with minimal groundworks required. Once the small concrete base and soakaway are prepared, the entire installation can often be completed within 3-5 days, including any necessary interior work.

Above: Installation of an ASHP unit is a relatively simple two-man job.

When ground source makes sense

There are some cases where ground source is the right tool for the job. If you have lots of outdoor space and a significant heating demand, a ground source heat pump can be a great option for you. Likewise, for large apartment buildings where a shared ground array can be installed for all the apartments to use (and split the cost). And if you prize your system absolutely minimizing energy consumption over cost and installation disruption then ground source heat pumps will be worth considering. 

96% of homes choose air source

In the UK's temperate climate, air source heat pumps emerge as the superior choice for most homeowners, offering an unbeatable combination of cost-effectiveness, ease of installation, space efficiency, and versatility. While ground source heat pumps may have a slight edge in energy efficiency during the coldest months, this marginal advantage is often outweighed by the significantly higher upfront costs and installation complexities. This is why most people in the UK choose an air source heat pump - 96% of projects funded by the Boiler Upgrade Scheme are air source compared to just 3% ground source.

By embracing air source heat pumps, British households can enjoy the benefits of clean, efficient heating while minimizing their financial burden and environmental impact. As the nation continues its journey towards a greener future, air source heat pumps stand as a compelling and accessible solution for those seeking to decarbonize their homes without compromising on practicality or affordability.

Interested in learning more about what a heat pump could do for your home? Get in touch to arrange a free consultation with one of our heating experts.