Comparison · 6 min read · Updated 2026-05-07
Air-to-water vs ground-source — which heat pump for which house
Cost, efficiency, ground-works and noise compared. A practical buyer's matrix and the climate threshold where ground-source pays off.
The short answer
- Air-to-water wins on capex (€10 k–18 k installed) and is fine
for >90% of European single-family houses, especially below 4 000 HDD₁₈ (most of central/western EU).
- Ground-source wins on long-run efficiency and works regardless
of outdoor weather, but adds €8 k–20 k of ground-works.
Why source matters
Heat pumps move heat from somewhere. Air-source pulls from outdoor air. Ground-source taps the soil 1–2 m down (horizontal field) or 50–150 m vertical boreholes. Soil temperature stays near 8–12 °C year-round in central Europe — much warmer than -10 °C air on the worst day of February.
That stability translates directly into SCOP:
| Climate | Air-water SCOP | Ground-source SCOP |
|---|---|---|
| Warmer (Athens) | 4.5–5.0 | 4.5–5.5 |
| Average (Strasbourg) | 4.0–4.6 | 4.5–5.5 |
| Colder (Helsinki) | 3.0–4.0 | 4.5–5.0 |
In Helsinki, going ground-source is roughly a 1.0-SCOP step up. In Vienna, the gap shrinks to 0.3–0.5 — often not worth €15 k of boreholes.
Capex breakdown
Typical 10–14 kW installation in Germany, 2026:
| Item | Air-water | Ground-source |
|---|---|---|
| Heat-pump unit | €5–8 k | €8–11 k |
| Buffer + DHW cylinder | €2–3 k | €2–3 k |
| Hydraulic + electrical | €2–3 k | €2–3 k |
| Ground works | — | €8–18 k |
| Total before subsidy | €10–18 k | €20–35 k |
Subsidies often favour ground-source — Germany BEG adds the "climate-friendly" 5% bonus, France MaPrimeRénov' Bleu band gives €11 000 vs €5 000 for air-water.
Decision matrix
Pick ground-source if any of these holds:
- You're building new or doing a deep renovation already moving earth
- Your climate is colder than 4 000 HDD₁₈ (Sweden, Finland, Baltics,
upland Czechia, north of UK)
- You'll stay in the property 15+ years
- Plot allows horizontal collector (1.5–2× heated floor area)
- High-temperature radiators kept (ground-source handles 55 °C output
more gracefully)
Pick air-water otherwise:
- Existing build, retrofit, plot constrained
- Climate is Average or Warmer
- You want lowest capex and shortest payback
- Underfloor heating exists or is being added
Noise
Air-water has a fan that runs continuously in winter — typically 50–58 dB outdoor sound power. Ground-source compressors live indoors in a utility room: 35–45 dB indoor, 0 dB outdoor. If your neighbours are close (urban Germany), this matters.
Hybrid as a third option
Hybrid systems pair an HP with a backup gas/oil boiler. Smart control optimises which to use based on tariff and outdoor temperature. Lower capex, but you're keeping fossil dependency and a chimney.
Recommended only if:
- Your existing fossil boiler is < 5 years old (don't bin it)
- Your radiators are sized for 70 °C output and you can't afford to
replace them yet
- You expect to do a deeper retrofit in 5–10 years