It's a little-known fact: the air/water and geothermal heat pumps we install to heat your home in winter can also cool it in summer. Here's how it works.
A heat pump can cool your home in two ways: active cooling and passive cooling. The whole difference comes down to one thing — does the compressor have to work, or not?
Active cooling: your air/water heat pump in reverse
The air/water heat pumps we install, such as the Buderus WLW176i AR, are reversible. In summer, the unit simply runs its cycle the other way around: instead of taking heat from the outside air to warm your water, it removes heat from your home and releases it outside. This is what we call active cooling. It produces cool water (around 18 °C) that flows through your existing underfloor heating or fan coils, gently lowering the indoor temperature — even and quiet, with no cold draught like a wall-mounted air conditioner.
The cooling function comes built into the heat pump as standard — it's not an add-on option. Switching to cooling mode is handled by the Logamatic BC400 controller, the same one that runs your heating and hot water. The only thing to add is a small dew-point sensor, which monitors humidity and prevents any condensation on the floor or the pipes. The compressor does run, so it draws some electricity — but far less than a classic air-conditioning system for the comfort you gain.
Passive cooling: the ground does (almost) all the work
A geothermal (ground-source) heat pump draws its energy from vertical boreholes drilled 80 to 150 metres deep. At that depth, the ground stays at a near-constant temperature all year — around 12 °C, whatever the weather above. In winter, the heat pump pulls warmth from that ground to heat your home. In summer, the logic reverses: your house (24–28 °C) is now much warmer than the ground, so the cool 12 °C earth becomes the perfect place to send the excess heat from your rooms. The same boreholes that warm you in January cool you in July.
This is where geothermal shines. With passive cooling (also called natural or free cooling), the cold brine from the boreholes is simply circulated through your underfloor system via a heat exchanger — carrying the heat of your home down into the ground. The compressor stays off: only a small circulation pump runs, so passive cooling uses just a few kilowatt-hours. Quiet, natural coolness for next to nothing.
In short: active or passive?
| Active cooling | Passive cooling | |
|---|---|---|
| How? | The heat pump reverses its cycle to produce cold | Cold from the ground (~12 °C) flows straight through the circuit |
| Compressor | Running | Off |
| Type of heat pump | Air/water and geothermal | Geothermal only |
| Energy use | Moderate — far less than a classic air conditioner | Almost none — just a circulation pump |
And the subsidy? Cooling is now allowed too
Here's the good — and recent — news: in Flanders, choosing a heat pump that can also cool no longer costs you your subsidy. Since July 2025, active cooling is fully allowed under the Mijn VerbouwPremie, whether the cooling is switched on in software or in hardware. So you get summer comfort and keep the grant. Amounts in Flanders, depending on your income: up to €6,000 for an air/water heat pump and up to €8,000 for a geothermal one.
Estimate your subsidy with our simulator
Thinking about a heat pump?
If you're considering an air/water or geothermal heat pump to heat your home in winter — and cool it in summer — mention it to us from the start. Our advisors carry out a free assessment. Call us on +32 15 62 70 80.