The water-to-water heat pump captures energy from groundwater, which stays stable at around 10 to 12°C all year long. This near-constant source gives it the highest COP of any heat pump, with no drop in performance in winter. It requires a usable aquifer, sufficient flow and an abstraction permit — we check everything before installing.
The figures that matter for a groundwater heat pump, studied and installed by our teams. Concrete benchmarks, not marketing.
The water-to-water heat pump posts the best efficiency of any heat pump. With groundwater permanently at 10–12°C, it delivers around 5 kWh of heat for 1 kWh of electricity — well above an air-to-water unit in winter.
Unlike outdoor air, which drops below zero, groundwater stays at a near-constant temperature. No frosting, no defrost cycles: performance doesn’t collapse in severe cold.
An abstraction well draws water from the aquifer, a return well sends it back after heat exchange. The water isn’t consumed, only cooled by a few degrees and returned underground.
Ideal as a low-temperature flow with underfloor heating. Possible with low-temperature radiators. The lower the flow temperature, the higher the COP climbs.
In summer, cool groundwater cools the home virtually for free (passive geocooling), without running the compressor. Summer comfort as a bonus to winter heating.
The borehole and probes are long-lasting; the indoor machine, sheltered from the weather, lasts longer than an exposed outdoor unit. Annual servicing is enough.
* Indicative values for a standard water-to-water installation. Actual performance depends on the aquifer’s flow, water quality and heating circuit — confirmed after the hydrogeological study.
No solution is perfect for every site. Here, honestly, is where the water-to-water heat pump excels and where it runs into constraints.
It comes into its own when the site offers a usable aquifer and you’re aiming for maximum efficiency over the long term. A few cases where it shines:
In a new build, low-temperature underfloor heating and an accessible aquifer unlock the full potential of water-to-water: the highest COP for a minimal bill.
If a groundwater aquifer with sufficient flow sits beneath your plot, water-to-water makes better use of this resource than any other heating solution.
In a well-insulated home converted to low temperature, water-to-water replaces an oil or gas boiler while sharply cutting the energy bill.
Without accessible groundwater, a geothermal heat pump captures energy from the ground through buried probes, with excellent efficiency. And for a tighter budget with no borehole, an air-to-water heat pump remains the simplest solution to install.
During a major renovation, the owners wanted to drop oil while aiming for maximum efficiency. The study confirmed an aquifer with sufficient flow at 9 metres. We carried out the twin borehole, obtained the abstraction permit and connected a water-to-water heat pump to the existing underfloor heating: constant performance and geocooling in summer.
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Water-to-water wins on raw efficiency, provided you have an aquifer. Compare it point by point with geothermal (ground collectors) and air-to-water, then open the solution that interests you.
| Critère | Water-to-waterVous êtes ici | GeothermalVoir la gamme → | Air-to-waterVoir la gamme → |
|---|---|---|---|
| Efficiency (COP/SCOP) | The highest | Very high | Good, drops in winter |
| Energy source | Groundwater 10–12°C | Ground via probes/collectors | Variable outdoor air |
| Winter stability | Constant | Very stable | Drops in severe cold |
| Abstraction works | Twin groundwater borehole | Borehole or ground collectors | None, outdoor unit |
| Site conditions | Usable aquifer required | Surface area or borehole possible | Almost anywhere |
| Installation cost | €€€€ — the highest | €€€€ — high | €€ — the gentlest |
| Ideal for | Aquifer available, max efficiency | Plot with no aquifer | Simple install, budget |
Energy drawn from the ground via collectors or probes, without pumping water. The alternative when the aquifer isn’t usable.
Compare with geothermal →No borehole, simple installation and a gentler budget. Efficiency drops in winter but stays very worthwhile.
Discover air-to-water →Air-to-air, air-to-water, geothermal, water-to-water: the full overview to choose the energy source right for your home.
See all types →The ideal low-temperature emitter for getting the best COP from a water-to-water heat pump. Even comfort, no visible radiators.
Discover underfloor heating →Regional grants, reduced VAT and benefits based on your income. The share covered on your water-to-water investment.
See heat pump aid →An overview of our heat pumps in Belgium: types, efficiency, installation, servicing and grants on one page.
Back to the heat pump guide →The price depends mainly on the twin borehole, the aquifer’s depth, the power output and the heating circuit. It’s the highest investment of all heat pumps, but the efficiency pays it back. Here are some benchmarks for an installed water-to-water unit.
See the detailed water-to-water price list →* Indicative ranges for an installed water-to-water system, excluding specific configurations. A costed estimate is provided after the hydrogeological study and the free quote.
A water-to-water heat pump pumps water directly from an aquifer through two wells (abstraction and return): the source is groundwater already at 10–12°C. A geothermal heat pump, on the other hand, captures heat from the ground via buried probes or collectors in which a fluid circulates — without pumping water. Water-to-water offers the best efficiency, but requires a usable aquifer.
Yes. Groundwater abstraction is governed by the Water Code in Wallonia (and by equivalent rules in Brussels and Flanders). You need an abstraction authorisation or declaration, sometimes accompanied by a water analysis. We handle this administrative file for you before any borehole.
Because the source is warm and stable: groundwater stays around 10 to 12°C year-round, even in the depths of winter. The pump therefore has only a small temperature gap to bridge, which maximises efficiency. An air-to-water unit, drawing from air that is sometimes below freezing, loses performance in the cold — not water-to-water.
It depends on the presence of an accessible aquifer and its flow. A prior hydrogeological study determines the depth, the available flow and the water quality. Without a usable aquifer, we turn to geothermal (ground probes) or air-to-water. We carry out this check before any commitment.
Yes, and it’s one of its strengths. In summer, cool groundwater enables passive geocooling: we cool the home by circulating this water through the floor, with the compressor barely running. Summer comfort as a bonus, for very low consumption.
Grants depend on your region and your income. In Wallonia, as in Brussels and Flanders, installing a high-performance heat pump qualifies for an energy grant, plus 6% VAT for homes over ten years old. On the higher investment of water-to-water, this aid significantly eases the bill. We put together the file for you.
Aquifer check, permit file, grants calculated, a single point of contact. Describe your project in under a minute.