The air-to-water heat pump is cheaper, installed faster and the standard case for heating replacement – in return, it needs a well-thought-out installation site and works less efficiently in winter. The brine-to-water heat pump with a geothermal probe costs significantly more with the drilling, but runs quieter, more efficiently and constantly for decades – and is funded more than twice as much in the Canton of Zurich. (As of: July 2026)
Key points in brief
- Both systems heat using the same principle – the difference is the heat source: outside air or ground.
- The outside air is tapped free of charge, but is coldest when the heating demand is greatest. The ground provides an almost constant temperature all year round.
- The geothermal probe is an investment for generations: The drilling outlasts the heat pump itself and is also available for the successor device.
- The Canton of Zurich promotes the geothermal probe much more strongly: CHF 6,800.– instead of a CHF 2,900.– flat rate (up to 15 kW, as of July 2026).
- In practice, the choice is often decided by the plot and neighbourhood – space for the drilling rig, water protection, noise situation – and not the catalogue.
How do the two systems work?
The basic principle is identical: A heat pump extracts heat from the environment and raises it to heating temperature using electricity. The difference lies in where it gets this heat.
The air-to-water heat pump uses the outside air. A fan draws air over a heat exchanger – set up as an outdoor unit in the garden or on the facade, as an indoor unit with air ducts or as a split system. The source is available everywhere and does not need to be tapped; in return, it fluctuates with the weather.
The brine-to-water heat pump gets the heat from the ground: One or more geothermal probes are drilled vertically into the ground, a water-antifreeze mixture (the «brine») circulates in them and brings the geothermal heat to the pump in the basement. At depth, there is an almost constant temperature all year round – the source knows no winter.
For the sake of completeness: There is also the water-to-water heat pump, which uses groundwater – the most efficient of all, but only at suitable locations and with its own permit. Where it is possible, it belongs in the clarification; for most single-family homes, the decision is between air and a geothermal probe.
The direct comparison
| Air-to-water | Brine-to-water (ground probe) | |
|---|---|---|
| Heat source | Outside air, weather-dependent | Ground, almost constant all year round |
| Efficiency | good; drops in the cold | higher, especially in winter |
| Investment | lower – no development effort | significantly higher – drilling is added |
| Incentives Canton of ZH (up to 15 kW) | CHF 2,900.– | CHF 6,800.– |
| Sound | Outdoor unit needs a well-thought-out location | practically inaudible (everything in the basement) |
| Space requirement | Footprint for the outdoor unit | Access for the drilling rig, afterwards invisible |
| Procedure | mostly notification procedure | Notification procedure + cantonal drilling permit |
| Lifespan of the source | – | Probe outlasts several device generations |
Simplified comparison; incentive rates as of July 2026 according to the cantonal programme (details and surcharges). The planning for the specific property is decisive.
Efficiency: Why the geothermal probe is ahead in winter
The difference in efficiency has a simple physical core: The smaller the temperature lift between the source and the heating, the less electricity the heat pump needs. And here lies the weakness of the air: It is exactly at its coldest when the house wants the most heat. The air-to-water heat pump therefore works the hardest in the coldest week of the year – it manages this without any problems, modern devices are designed for our climate, but it needs noticeably more electricity for it.
The geothermal probe does not have this problem: At depth, the temperature remains stable, whether there is a heatwave or a bise outside. Calculated over the year, the brine-to-water heat pump therefore gets more heat out of the same kilowatt hour of electricity – how much is described by the annual performance factor (JAZ), the central efficiency indicator of both systems.
For the combination with photovoltaics, by the way, this changes little in terms of logic – both systems benefit equally from their own solar power. The geothermal probe simply needs less of it overall.
Costs and incentives: The calculation with the drilling
When it comes to price, the picture is clear, even without Swiss franc amounts: The air-to-water heat pump is the cheaper purchase because its source costs nothing. With the geothermal probe, the drilling is added – a significant item that significantly increases the investment. What the systems cost in detail is covered by the cost guide; here, the structure of the calculation counts.
Because two items work in favour of the geothermal probe:
The incentives. The Canton of Zurich pays more than double the air-to-water flat rate for the brine-to-water heat pump at CHF 6,800.– (CHF 2,900.–, each up to 15 kW; larger systems receive surcharges per kW). The difference covers part of the drilling costs – the canton specifically promotes the more efficient system. Rates, conditions and the application process are in a separate article; as always: application before the start of construction.
The lifespan of the probe. You buy the drilling once: A professionally installed geothermal probe significantly outlasts the heat pump itself and is also available for the successor device. For the second heating replacement in twenty years, the geothermal probe property only pays for the device – the source is already there. Whoever thinks in generations therefore does not calculate the drilling over a device lifespan, but over the house.
Nevertheless, the honest classification remains: For many budgets, the air-to-water heat pump is the realistic choice, and it is a good one – the majority of heating replacements in the region are built with air-to-water, for understandable reasons.
Space, noise, permit: The practical differences
Noise is the everyday topic of the air-to-water heat pump: The fan of the outdoor unit is audible, and the noise protection regulations set binding limits towards neighbours. With a well-thought-out location, this is solvable – but it is a planning issue that belongs on the table early on. The geothermal probe system simply does not have it: Everything is in the basement, nothing can be heard or seen outside.
Space is needed by the geothermal probe once during construction for this: The drilling rig must be able to get onto the property and stand there. In densely built-up neighbourhoods, narrow gardens or on hillsides, the probe occasionally fails not because of money, but because of access – the specialist planning clarifies this on site before calculations are made.
In terms of the procedure, both run via the notification procedure in the Canton of Zurich; the geothermal probe additionally needs the cantonal water protection permit for the drilling. Whether drilling is allowed at the location at all is shown by the cantonal heat utilisation map – in groundwater protection zones, probes are restricted or excluded. The specialist company also checks this early on, because it sometimes decides the system question by itself.
When does which system fit?
The air-to-water heat pump fits if the budget is in the foreground, the heating replacement has to go quickly, a reasonable installation site with a distance to the neighbour is available – or the property is simply not accessible for the drilling rig. It is the proven standard case, and properly planned, you hardly hear it.
The geothermal probe fits if you think long-term – own house, next device generation included –, if the noise situation is sensitive (dense neighbourhood, sensitive neighbourhood, core zone) or if efficiency and low operating costs have priority. The higher cantonal incentives take away some of the horror of the drilling.
And what if both were possible? Then the full cost calculation over the lifespan is worthwhile instead of the price comparison on the day of sale – with incentives, operating costs and the second device generation. Exactly this calculation belongs in a reputable heating replacement consultation; across the board, neither of the two systems wins.
In consultations, we regularly experience that the system question is ultimately not decided in the brochure, but in the garden. The conversation starts with efficiency numbers and ends with two very practical questions: Where exactly should the outdoor unit stand without radiating sound to the neighbour's seating area – and would a drilling rig even get onto the property? There are neighbourhoods where the second question buries the probe before anyone has talked about money, and terraced house locations where, conversely, the noise complicates the air-to-water solution so much that the drilling is suddenly the simpler answer. Our advice therefore: Have both questions checked on site before you fall in love with a system – the property surprisingly often has the last word in this decision.
Frequently asked questions
Can drilling be done on every property?
No – water protection and the subsoil are decisive: In groundwater protection zones, geothermal probes are restricted or impermissible, and the drilling rig needs access to the property. The cantonal heat utilisation map gives the first answer; the binding clarification belongs at the beginning of the planning.
How long does a geothermal probe last?
Significantly longer than the heat pump itself – a professionally installed probe is also available for the next device generation. The drilling is therefore an investment in the house, not in a single device.
Is an air-to-water heat pump too weak in winter?
No – modern devices are designed for the Swiss climate and heat reliably even at severe sub-zero temperatures. They then simply need more electricity because the source is cold; this is an efficiency issue, not a functional one.
Can I switch from air-to-water to a geothermal probe later?
Technically yes, economically rarely sensible – the drilling is most worthwhile when it is created right at the time of the heating replacement. Whoever chooses air-to-water today usually also chooses air-to-water again for the next replacement.
What about groundwater heat pumps?
Where groundwater is available in a suitable quantity and quality, water-to-water systems are the most efficient – the canton provides incentives for them equally as high as for geothermal probes. They need their own concession or permit and a careful clarification; they are not a standard case for a single-family home.
Free initial consultation
Air or probe? Your property has a say in the decision.
We check the location, noise situation and drilling feasibility on site and honestly calculate both systems – with incentives and operating costs, not just with the purchase price.
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Swissolar-certified specialist company · ESTI installation authorisation (Art. 14 NIV) · in Zurich since 2017 · over 150 systems completed · a personal answer from the specialist company, no call centre
Sources: Canton of Zurich (incentive programme 2026, notification procedure, heat utilisation); Swiss Heat Pump Association FWS (system basics); empirical values from the project practice of ecoEn GmbH, Zurich region.
Last updated: 9 July 2026 · Author: ecoEn editorial team
