Choosing an air source or ground source heat pump

Choosing a new heating system for your home is a significant decision, and heat pumps are increasingly becoming the smart choice for UK homeowners. These systems offer an efficient, lower-carbon alternative to traditional boilers, extracting renewable heat from the environment to warm your home and provide hot water. This guide cuts through the noise to help you understand the fundamental differences between air source and ground source heat pumps, their costs, efficiency, and suitability for your property, empowering you to make informed decisions about your home's energy future.

Understanding heat pumps: the basics

Heat pumps operate on a simple, yet highly effective principle: they move heat rather than generate it by burning fuel. This makes them significantly more energy-efficient and results in lower carbon emissions compared to gas or oil boilers. While both air source and ground source systems achieve this, they differ in where they extract that renewable heat.

How air source heat pumps work

An air source heat pump (ASHP) extracts heat from the outside air, even when temperatures are very low. It uses a fan to draw air over a heat exchanger coil containing a refrigerant. This refrigerant absorbs heat from the air, even at low temperatures, and then compresses it to increase its temperature further. This higher-temperature heat is then transferred to your home's heating and hot water systems. The outdoor unit typically resembles an an air conditioning unit.

How ground source heat pumps work

A ground source heat pump (GSHP) harnesses the more stable temperature beneath the earth's surface. It does this via a network of pipes, known as a ground loop, buried either horizontally in trenches or vertically in boreholes. A fluid circulating through these pipes absorbs heat from the ground, which then passes through a heat exchanger in the heat pump. Like an ASHP, the heat pump compresses this heat to raise its temperature before distributing it throughout your home. Ground temperatures remain relatively constant year-round, typically remaining stable below one metre of depth, even when the air temperature is freezing.

Key differences: installation, space, and performance

The choice between an air source and ground source heat pump often comes down to practical considerations related to your property and how each system performs under varying conditions.

Installation complexity and disruption

Installing an air source heat pump is generally less complex and disruptive than a ground source system. The main components are an outdoor unit and an indoor unit, connected by refrigerant lines. While some pipework and electrical upgrades may be necessary, significant excavation is usually not required.

Ground source heat pump installation, however, involves substantial groundwork. Horizontal ground loops require digging extensive trenches across a large area of your garden, while vertical loops necessitate drilling boreholes deep into the ground. This process is considerably more disruptive and can take longer to complete.

Space requirements for each system

Space is a critical factor. Air source heat pumps need a clear, unobstructed area around the outdoor unit for optimal airflow. This unit can be placed in a garden, on a wall, or even on a flat roof.

Ground source heat pumps demand significantly more space for their ground loops. A horizontal system for a typical home might need a substantial outdoor area. If sufficient land isn't available, vertical boreholes are an option, but these still require access for drilling equipment and can be more costly.

Efficiency in the UK climate

Heat pumps are remarkably efficient, often achieving efficiencies (measured as a Seasonal Coefficient of Performance, or SCOP) of 300% or more, meaning they produce 3 or more units of heat for every unit of electricity consumed. This contrasts sharply with traditional gas boilers.

Ground source heat pumps generally offer more consistent efficiency year-round due to the stable temperatures of the ground. They don't have to work as hard to extract heat during colder months. Air source systems, while still effective in cold weather, can see their efficiency drop when outdoor temperatures are very low, as there is less heat available in the air to extract. Modern ASHPs are designed to operate effectively in typical UK winter temperatures, which rarely drop below freezing for extended periods.

Costs and financial considerations

The financial outlay for a heat pump system involves both upfront installation costs and ongoing running costs, which can be significantly offset by government incentives.

Upfront installation costs

The initial investment for a heat pump varies considerably between the two types. Air source heat pumps typically cost between £7,000 and £15,000 to install. Ground source systems are substantially more expensive, with the higher end reflecting the cost of drilling boreholes. These figures are before any grants are applied.

Running costs and potential savings

While electricity is generally more expensive per unit than gas, the high efficiency of heat pumps means they can still offer considerable running cost savings over the long term, especially when replacing older, inefficient fossil fuel boilers. The average UK home uses around 9,500 kWh of gas per year for heating1. By converting this demand into highly efficient heat pump operation, homeowners can reduce their overall energy consumption for heating. Running costs are influenced by factors such as your home's insulation, the size of the property, and your specific energy tariff.

UK government grants and incentives

The UK government actively encourages the adoption of heat pump technology through financial incentives. The Boiler Upgrade Scheme (BUS) offers grants of £7,500 towards the installation of both air source and ground source heat pumps for eligible homeowners in England and Wales. For households in England and Wales currently on heating oil, an uplifted grant of £9,000 is available until March 2027. To be eligible for the BUS, installations must be carried out by an MCS (Microgeneration Certification Scheme) certified installer. It is important to note that Fuse Energy does not install heat pumps or handle BUS applications; customers should seek a certified third-party installer for this. All heat pump installations in the UK must also comply with Building Regulations, particularly concerning energy efficiency and safety.

Which heat pump is right for your UK home?

Making the right choice depends on a careful assessment of your property, budget, and long-term energy goals.

Suitability for different property types

Air source heat pumps are often a more suitable choice for a wider range of UK homes, particularly those with smaller gardens or limited outdoor space where extensive excavation isn't practical. They can be a good fit for many existing properties, provided there's adequate space for the outdoor unit and the home is well-insulated.

Ground source heat pumps are ideal for new builds or larger properties with ample land available for horizontal ground loops. Their consistent performance makes them attractive, but the significant installation costs and disruption mean they are best suited to properties where these factors are less of a barrier. Regardless of the type, assessing your home's insulation levels and existing heating system compatibility is crucial to ensure optimal performance.

Long-term investment and environmental impact

Investing in a heat pump is a strategic move towards greater energy independence and reduced environmental impact. These systems play a vital role in the phase-out of fossil fuel boilers, contributing to a future with lower carbon emissions. By choosing a heat pump, you can reduce your long-term energy bills and gain greater control over your home's heating. This aligns with a vision of energy abundance, moving away from reliance on finite fossil fuels.

Making an informed decision

To make an informed decision, evaluate your home's heat demand and current insulation. Understand the fundamental differences between air source and ground source heat pumps, then obtain detailed quotes from MCS-certified heat pump installers. Research and apply for relevant UK government grants and financial incentives, and compare the long-term running costs, efficiency, and environmental impact for your specific situation. Fuse Energy supports homeowners with electricity supply and smart tariffs for their heat pump homes, empowering transparent energy management and customer control.

References

1. Ofgem. Review of Typical Domestic Consumption Values