Ground source or air-to-water heat pump? A 2026 comparison

In a new detached house, a ground source heat pump typically costs €18,000–25,000 and an air-to-water heat pump €10,000–15,000, so the gap in capital cost is about €5,000–10,000. In running costs the difference in a new, energy-efficient house is only about €100–200 a year in favour of ground source. In a small or mid-sized new build the choice is therefore finely balanced and is settled by the plot, the service life and the resale value. In a large house or a building, ground source is the clear winner.

How do the two systems differ?

• A ground source heat pump draws heat stored in the bedrock or the soil through a borehole or a ground loop. The temperature of the heat source stays steady all year round, so output does not depend on the frost.
• An air-to-water heat pump collects heat from the outdoor air with an external unit and transfers it into the house’s water-based heat distribution. In hard frost its efficiency falls and the unit leans more heavily on its electric immersion heater.

Which has the better efficiency?

A ground source pump’s SCOP is typically 3–4 regardless of outdoor temperature. A well-designed air-to-water system reaches a SCOP of 3.5–4, but achieves 2.5–3.5 over a year in practice, dipping briefly to 1.5–2.2 in hard frost (below −20 °C). The old claim that air-to-water pumps do not work in Finnish winters no longer holds: today’s units run down to −25 °C and even −30 °C, though output falls.

How big is the difference in running costs?

A worked example: a new 150 m² house needs about 12,000–15,000 kWh a year for heating and hot water. A ground source pump buys about 3,500–4,300 kWh of that as electricity, an air-to-water pump about 4,000–5,000 kWh. At 14 cents/kWh all-in, the difference is about €100–200 a year – so recovering the €5,000–10,000 capital gap on energy savings alone often takes over 20 years in a new, airtight house.

The picture changes as the heat demand grows. In a large house or a building using more than 25,000 kWh a year, the gap widens to €400–800 a year – and the longer service life of ground source tips the whole-life calculation clearly in its favour. Use an all-in electricity price of 12–15 cents/kWh in your own sums, not the crisis prices of 2022–2023.

What about spot-priced electricity and winter peaks?

Both suit price-led control on a spot-price tariff: water-based underfloor heating in a concrete slab acts as a heat store you can charge during the cheapest hours. Winter peaks, though, favour ground source: when prices peak in January and February, an air-to-water pump is at its least efficient because of the frost, while ground source delivers the same heat on less electricity.

Plot, installation, servicing and service life

• An air-to-water pump needs only a spot for the external unit against the house wall, so it suits even a small plot. The external unit is visible, makes some noise when running, and needs an annual check and filter cleaning (about €100–200 a year). Its service life is typically 15–20 years.
• Ground source requires drilling a borehole or excavating a ground loop, and the drilling rig has to be able to reach the plot. The finished system sits indoors, runs quietly and is all but maintenance-free. The pump lasts 20–25 years and the borehole about 50.
• Rock conditions, a groundwater area or a very tight plot can rule out drilling – in which case an air-to-water pump is in practice the only one of the two available.

On permits: a ground source borehole needs a permit from municipal building control, handled alongside the house's building permit in a new build. An air-to-water pump involves no drilling, which simplifies the project, particularly in renovations.

Which should you choose?

Choose an air-to-water pump when the budget is below roughly €15,000, the house’s energy demand is low, or the plot cannot be drilled or is not worth drilling. In a new, airtight house the lower purchase price weighs heavily, because there is little energy left to save.

Choose ground source when you are building a large house or a building, the heat demand is high, or you want the longest service life and the steadiest output. Ground source is the most popular main heating choice among Finnish self-builders and lifts the value of the property – a large log house with a high heating demand is a typical case for it. Both systems work best paired with water-based underfloor heating, so heat distribution does not narrow the choice.

Sales figures show the decision splits self-builders down the middle: in 2025 Finland sold roughly 7,000 ground source heat pumps and about the same number of air-to-water pumps. It is hard to choose wrongly – with either, heating costs are a fraction of direct electric heating.

• Capital cost in a 2026 new build: ground source €18,000–25,000, air-to-water €10,000–15,000 – a gap of €5,000–10,000.
• SCOP: ground source 3–4 whatever the frost; air-to-water 2.5–3.5 in practice, with efficiency falling in cold weather.
• In a new 150 m² house the difference in running costs is only about €100–200 a year – payback on the price gap often takes over 20 years.
• In a large house or a building the gap widens to €400–800 a year, and ground source wins over the whole life cycle.
• Service life: ground source pump 20–25 years and borehole about 50; air-to-water 15–20 years with annual servicing at about €100–200.
• Run your comparison on an all-in electricity price of 12–15 cents/kWh.