A reversible heat pump can cool, and most air-to-water models sold in Europe contain the four-way valve needed to do it. Through underfloor circuits the flow temperature must stay above the room dew point — typically 16–20 °C — which removes only 15–30 W/m², about a quarter of the floor's heating output. Fan coils cool much harder because they also dehumidify, but need a condensate drain.
Can an air-to-water heat pump run in reverse?
Yes, if it is a reversible model. A four-way valve swaps the roles of the two heat exchangers so the indoor side absorbs heat and the outdoor coil rejects it — the same refrigerant circuit, running backwards. Most European air-to-water units are supplied reversible; the function is usually enabled in the controller and requires a room or dew point sensor and, often, a cooling-capable circulation strategy.
What a heat pump cannot do is cool a house that was never prepared for it. Cooling is not simply heating with a minus sign: the water is now colder than the air, which means every uninsulated pipe, valve and manifold in the building becomes a condensation risk.
Why is underfloor cooling limited by dew point?
Because the floor surface must never fall below the dew point of the room air, or it will sweat. At 26 °C and 60% relative humidity the dew point is about 17.6 °C; at 25 °C and 55% it is around 15 °C. Controllers therefore hold the cooling flow temperature at 16–20 °C and measure humidity continuously, raising the flow if the room air gets damp.
That temperature ceiling caps the output. A floor at 20–21 °C in a 26 °C room removes roughly 15–30 W/m² — about a quarter of what the same floor delivers in heating mode. It is genuine, silent, draught-free comfort that will take 2–4 °C off a hot afternoon in a well-shaded house. It is not air conditioning, and it will not rescue a west-facing room with large unshaded glazing.
| Method | Typical cooling output | Dehumidifies? | Needs condensate drain |
|---|---|---|---|
| Underfloor circuits | 15 – 30 W/m² | No | No (must avoid condensation) |
| Wall or ceiling radiant panels | 40 – 70 W/m² | No | No |
| Fan coil units | 1 – 5 kW per unit | Yes | Yes |
| Air-to-air split | 2 – 7 kW per unit | Yes | Yes |
| Ground source passive cooling | 10 – 25 W/m² | No | No |
What has to be right before you cool?
- Insulated pipework and manifolds throughout, including in warm plant rooms, or the primary circuit sweats where you cannot see it.
- A dew point sensor in the reference room and, for underfloor systems, at each manifold.
- A cooling-capable buffer strategy. Chilled water and hot water cannot share an uninsulated store, and the buffer tank must be vapour-sealed if it is used in cooling mode.
- Hot water priority that still works. The unit cannot cool and charge the cylinder at once, so the control must switch cleanly between modes.
- Screening on the outdoor unit's discharge. In cooling mode it blows hot air, not cold — do not aim it at a terrace or a neighbour's window.
Does cooling wreck efficiency, or the grant?
Cooling efficiency is rated separately as SEER under EN 14825, and reversible air-to-water units typically achieve SEER 4–6 with underfloor circuits, helped by the high water temperature. Running costs are modest for radiant cooling precisely because the output is modest.
Grants are the bigger question. Most national heat pump subsidies are written for space heating and hot water, and some exclude or ignore the cooling function entirely; a few require the installer to demonstrate that cooling does not compromise the heating design. Ask before you order, and see which European countries offer heat pump grants in 2026?.
Which cooling approach should I choose?
If you already have underfloor heating, enable radiant cooling: the hardware is largely in place and the comfort is excellent. If you need real temperature control in a hot climate or a glazed room, fit fan coils on the same water circuit — they cool and dehumidify, and they double as fast-response heating in winter. If the building has radiators only, cooling through them is not practical; a separate air-to-air split is the pragmatic answer, as discussed in heat pump with underfloor heating vs radiators.
In Solimpeks’ experience the cooling installations that go wrong are almost never let down by the machine; they are let down by uninsulated pipework and missing dew point control, both decided long before the heat pump is ordered.
A ground source system deserves a special mention: it can cool passively, circulating water through the ground loop with the compressor switched off, at a fraction of the electricity of any active method.
Frequently asked questions
Do all heat pumps cool as well as heat?
No. Only reversible models with a four-way valve can cool, and the function must be enabled and commissioned. Many monobloc units sold for heating-only markets are supplied without it, so check the model designation rather than assuming.
Can underfloor heating be used for cooling?
Yes, at 16–20 °C flow, giving roughly 15–30 W/m². The limit is the room dew point: if the floor surface goes below it, condensation forms. A humidity sensor and dew point control are mandatory, and all pipework must be insulated.
Is heat pump cooling cheaper than air conditioning?
Radiant cooling through a floor uses very little electricity because the output is small and the water temperature is high — SEER 4–6 is typical. A split air conditioner removes far more heat per unit but works harder to do it, so the comparison depends on how much cooling you actually need.
Does cooling shorten the life of a heat pump?
No. Reversible operation is a normal duty for the compressor and the four-way valve, and the summer cooling season is short in most of Europe. The real risks are condensation damage to uninsulated pipework and mould, not mechanical wear.