What Is a Ground Source Heat Pump?

By Cormac Breen

Content Manager

Cormac is Selectra.ie's energy expert along with being the chief content and editorial manager for the website. His aim is to help find the best deal for you and your home energy needs so that you save money on your annual bills. His knowledge and experience of the Irish energy market allows him to offer the best advice and insight into current prices, emerging trends and overall energy saving tips.

A ground source heat pump (GSHP), also known as a geothermal heat pump, is a highly efficient, renewable heating system that harnesses the relatively constant solar energy stored beneath the earth's surface. It works by circulating a thermal fluid through a buried network of pipes (a ground loop) to extract this stable heat. This heat is then transferred and compressed to a higher temperature to provide a building's central heating and hot water.

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What Is a Ground Source Heat Pump?

A ground source heat pump is a central heating system that uses the earth as a heat source and a heat sink.

It uses buried piping to tap into the shallow subsurface, where temperatures are stable regardless of extreme air temperature fluctuations.

This constant temperature ensures the system operates with high efficiency throughout all seasons, providing 100% of a property's heating and hot water needs.

How Does a Ground Source Heat Pump Work?

The operation of a GSHP is based on the vapour compression refrigeration cycle, similar to other heat pumps, but with a unique heat collection mechanism.

The process is as follows:

1. Ground Loop (Collector Array): A mixture of water and anti-freeze (thermal transfer fluid or brine) circulates through buried pipes. This fluid absorbs the stable, low-grade thermal energy from the ground. The loop can be horizontal (buried in trenches) or vertical (inserted into deep boreholes).
2. Evaporator: The warmed fluid enters the indoor unit and passes through a heat exchanger, transferring its heat to a liquid refrigerant, causing the refrigerant to evaporate into a low-pressure gas.
3. Compressor: An electric compressor pressurises the gaseous refrigerant, which dramatically increases its temperature.
4. Condenser (Heat Exchanger): The hot, high-pressure gas transfers its heat to the water in your home's central heating system (radiators or underfloor heating) and hot water cylinder. The refrigerant then condenses back into a liquid.
5. Expansion Valve: The liquid refrigerant is depressurised, lowering its temperature, and sent back to the ground loop to restart the process.

This process is remarkably efficient, often yielding a COP of 4.0 or higher, meaning 1 kW of electrical energy consumed by the compressor can deliver 4 kW or more of useful heat energy.

How Much Does a Ground Source Heat Pump Cost?

The ground source heat pump Ireland cost is notably higher than for air source systems, primarily due to the extensive and costly groundwork required for the ground loop installation.

• Total Installed Cost (Excluding Grants): For an average Irish home, the supply and full installation of a GSHP system typically ranges from €17,000 to €28,000.
• Grant Support: The Sustainable Energy Authority of Ireland (SEAI) offers grants of up to €6,500 for the heat pump system installation.
• Cost After Grant: The net cost to the homeowner typically ranges from €10,500 to €21,500, excluding necessary insulation or emitter upgrades.
• Running Cost Savings: Running costs are usually lower than air source systems. Average annual running costs for a well-insulated home often range from €500 to €900.

Are Ground Source Heat Pumps Worth It?

Yes, ground source heat pumps are generally worth the significant investment for homeowners with suitable land, particularly when building a new home or undertaking a major renovation.

The primary factors justifying the cost include:

• Lowest Running Costs: The stable ground temperature ensures the highest possible efficiency (SCOP), leading to the lowest heating bills over the long term.
• Longest Lifespan: The indoor unit typically lasts 20 to 25 years, while the buried ground loop infrastructure can last for 50 years or more.
• Silent Operation: There is no large outdoor fan unit, meaning the system is virtually silent outside the home.
• Increased Property Value: Installation results in a substantial increase in the home’s energy rating (EPC).

How Do Ground Source Heat Pumps Compare to Other Heating Systems?

Assuming a reasonably well-insulated home requires an annual heat demand of 15,000 kWh, the table below shows how different heating methods translate into annual energy costs based on efficiency and current unit prices in 2025.

This comparison highlights the low running costs that make the Ground Source Heat Pump a superior long-term financial choice.

Based on Oil price of €0.97/litre. This annual cost for Gas does not include the standing charge.

Long-Term Cost Analysis of a Ground Source Heat Pump

While the initial cost of a ground source heat pump (GSHP) is high, its value proposition is best demonstrated by comparing the total expenditure over a long period, such as 25 years.

Assuming a reasonably well-insulated home with an annual heat demand of 15,000 kWh, the GSHP offers the lowest total cost of ownership compared to fossil fuel and other electric heating options.

The following table illustrates the projected full life-cycle cost based on current energy prices in 2025 (Gas: €0.1347/kWh; Electricity: €0.3634/kWh; Oil: €0.98/litre):

This analysis does not account for the impact of future carbon tax increases, which will disproportionately raise the cost of running fossil fuel boilers (Oil and Gas).

Where Can I Buy Ground Source Heat Pumps in Ireland?

Procurement is heavily dependent on specialist expertise due to the complex groundworks involved.

Systems must be supplied and installed by certified professionals.

• Specialised Contractors: Companies providing full-service design, drilling/trenching, installation, and commissioning are the main channel.
• Major Brands: Leading international brands with strong market presence in ground source heat pump Ireland include NIBE, Daikin, Mitsubishi, Kensa, and WaterFurnace.
• Crucial Note: Always use an SEAI-registered contractor to guarantee system eligibility for the €6,500 grant.

Ground Source Heat Pump Hardware Costs

The heat pump unit itself is similar in cost to a high-end air source unit, but the total hardware cost is dominated by the ground collectors.

• GSHP Unit Only: The standalone indoor unit typically ranges from €4,000 to €12,000.
• Special Hot Water Cylinder: A heat pump-compatible cylinder is required, adding an estimated €1,500 to €2,000.
• Ground Loop Materials: The cost of the specialised pipework, thermal fluid, and connection hardware depends on the type (horizontal trenching is cheaper than vertical boreholes).

How Do I Optimise the Efficiency of My Ground Source Heat Pump?

GSHPs, like all heat pumps, operate most efficiently when producing heat at lower flow temperatures (35°C to 45°C).

For this to be effective, the property must be extremely well-insulated to prevent rapid heat loss.

The "fabric first" approach is essential, especially when retrofitting older homes:

• Loft Insulation: Ensure a minimum depth of 300mm to mitigate heat loss through the roof.
• Wall Insulation: For solid-wall properties (common in older Irish homes), this requires either External Wall Insulation (EWI) or Internal Wall Insulation (IWI). Cavity walls must be fully filled.
• Air Tightness and Glazing: Upgrading to high-performance double or triple glazing and thoroughly sealing all air leaks (draught-proofing) is mandatory for achieving low heat demand.
• Heat Emitter Upgrades: Traditional radiators designed for high boiler temperatures must be replaced with oversized, low-temperature radiators or, ideally, underfloor heating to effectively deliver heat at the GSHP's optimal flow temperature.

What Are the Downsides of a Ground Source Heat Pump?

The following table details the key drawbacks that potential users must consider, alongside effective strategies to mitigate their impact.

Why Is My Electric Bill So High with a Ground Source Heat Pump?

While GSHPs are inherently efficient, unexpected high electricity bills typically stem from non-optimised system use or poor building fabric performance.

The issue usually lies in:

• Inadequate Insulation: If the house loses heat faster than the GSHP can provide it at an efficient low temperature, the system runs longer and harder, consuming excess energy.
• Incorrect Sizing: An incorrectly sized system will run inefficiently, leading to higher electricity use.
• Improper Usage Pattern: Running the system intermittently or setting drastic temperature setbacks forces it to engage less efficient electric backup heating to quickly reheat the home.

How Do I Optimise a Ground Source Heat Pump?

GSHPs adhere to the principle of maintaining a steady, consistent temperature.

The key operational advice is:

• Maintain a Consistent Temperature: Do not use the heat pump like an old boiler by turning it on only when heat is needed. Run it continuously to maintain the desired comfort level (19°C to 21°C).
• Optimise Flow Temperature: The system should be set to the lowest possible water flow temperature (often 35°C to 45°C) that keeps the house comfortable. This is the single biggest factor in maximising the system's efficiency.

By Cormac Breen

Content Manager

Cormac is Selectra.ie's energy expert along with being the chief content and editorial manager for the website. His aim is to help find the best deal for you and your home energy needs so that you save money on your annual bills. His knowledge and experience of the Irish energy market allows him to offer the best advice and insight into current prices, emerging trends and overall energy saving tips.