Ask most British homeowners whether their heat pump can cool their home in summer and you’ll get a blank look. Ask their installer and you’ll often get the same response, or a slightly defensive “well, technically it can, but…” Most air source heat pumps sold in the UK are reversible — the refrigerant cycle can run in reverse to extract heat from inside your home and dump it outside, exactly like an air conditioner. But for years, this capability sat essentially unused.
That’s changing fast. The summers of 2024 and 2025 were the hottest on UK record. Cooling demand that was once a luxury for Mediterranean climates is becoming a practical question for British households, especially in well-insulated homes where keeping heat in during winter means keeping it in during July too.
How Reversible Heat Pumps Actually Work
A standard air source heat pump moves heat from outside air into your home using a refrigerant cycle. In heating mode, the outdoor unit extracts heat from cold outside air (even at -10°C, there’s usable heat) and pumps it inside. In cooling mode, the cycle simply runs backwards: the unit extracts heat from inside your home and dumps it into the warmer outside air.
This is the same principle as every air conditioner ever built. The difference with a heat pump is that the refrigerant cycle is designed to operate efficiently in both directions, whereas a standard AC unit only cools.
The question of whether your specific heat pump can actually run in cooling mode comes down to a few things: the heat pump unit itself (almost all modern inverter-driven units support it), the indoor distribution system, and whether your installer commissioned the cooling function.
Wet underfloor heating (UFH): Can run in active cooling mode. Water at around 16–18°C circulates through the floor, drawing heat from the room. It’s gentle — don’t expect the blast of cold air you’d get from an AC — but over a few hours it genuinely lowers room temperature. Radiant cooling from a cool floor surface is comfortable and avoids the draughts and noise of forced air systems.
Radiators: Generally not suitable for active cooling. Running cool water through radiators risks condensation on metal surfaces, particularly in humid summer air. Some systems use dehumidification controls to manage this, but most installers recommend against it for standard UK radiator installations.
Fan coil units: Work well for both heating and cooling. If you have fan coils rather than radiators — more common in new builds and renovation projects — cooling through the same distribution system is straightforward.
Passive vs Active Cooling
There are actually two modes of cooling available on some heat pump systems, and they’re quite different in cost and efficiency.
Passive (or natural) cooling uses a simpler mechanism: the heat pump’s refrigerant circuit circulates cool refrigerant from the outdoor ground-source loop (ground source pumps only) or through the heat exchanger without running the compressor. Because the compressor isn’t running, it uses very little electricity — typically just the pump circulation power. Ground source heat pump owners in the UK can often access this, but it requires specific system design.
Active cooling runs the full refrigerant cycle in reverse. It’s more effective — can cool down a well-insulated home by 4–6°C on a hot day — but uses electricity at roughly the same rate as heating (with a seasonal COP of around 3–4, so it’s still far more efficient than electric resistance cooling). This is what most air source reversible heat pumps offer.
What Enabling Cooling Actually Involves
If your heat pump unit is a reversible model (check the spec sheet — the technical documentation will list it) but cooling wasn’t commissioned during installation, here’s what enabling it typically requires:
Controls: Your existing controller or thermostat may need an upgrade to support cooling mode. Some manufacturers provide this via a software unlock; others require a hardware controller upgrade. Budget £150–400 for controls if needed.
Commissioning: A qualified installer needs to configure the system parameters for cooling — flow temperatures, setpoints, defrost logic, and condensate drainage if your indoor unit has a drip tray. This is typically a half-day job: £200–400 for a return visit.
Condensate drainage: When your heat pump cools your home, indoor components will collect condensate (moisture from the air). This needs somewhere to drain. Many installations have this already (your boiler had the same requirement), but some don’t — retrofitting a condensate drain can add cost.
Underfloor heating manifold valves: If you have UFH and your manifold valves were fitted for heating only, they may need adjustment to allow cooling flow rates.
Total cost to enable cooling on an existing reversible heat pump: typically £350–900, depending on what’s already in place. For a system not yet installed, specifying cooling at the point of installation adds very little to the cost and saves the return visit.
Does It Actually Work in a UK Home?
Fair question, given the UK’s historically mild summers. The honest answer is: it depends on the house.
A well-insulated, low-mass modern home (the kind that retains heat in winter) can overheat significantly during UK heat events. July 2025 saw several days above 35°C in the south-east, and a well-insulated house with south-facing glazing can hit 28–30°C+ inside without any cooling. Active cooling in this scenario genuinely makes the house habitable.
An older, poorly insulated home with single glazing loses heat freely — the natural ventilation that makes it draughty in winter also keeps it cooler in summer. Cooling via a heat pump may be less effective because heat infiltration through the fabric exceeds what the heat pump can extract.
The Boiler Upgrade Scheme (BUS) grant currently covers air source heat pump installation but doesn’t specifically require or exclude cooling capability. If you’re applying for BUS support, specifying a reversible unit with cooling commissioning is simply a matter of talking to your MCS-certified installer.
Running Costs
Here’s a rough guide for active cooling electricity costs in the UK in 2026, assuming an electricity rate of approximately 25p/kWh (variable by tariff):
| Home size | Cooling load on a hot day | Estimated hourly running cost |
|---|---|---|
| 2-bed flat/house | 1–2 kW | 6–17p/hour |
| 3-bed semi | 2–3 kW | 13–25p/hour |
| 4-bed detached | 3–5 kW | 19–42p/hour |
For context: running active cooling for 8 hours on the hottest days would cost roughly £1–3 per day for a typical three-bed house. It’s not free, but it’s comparable to running a portable AC unit that’s far less efficient.
Smart tariffs like Octopus Agile let you cool your home during cheap overnight or early-morning periods, pre-cooling the building before the heat of the day — thermal mass in the floors stores the coolth. If you have a smart EV tariff or home battery, the same principle applies.
For most homes with an existing reversible heat pump and underfloor heating, the cost of enabling cooling is well worth it given the direction of UK summers. Worth having the conversation with your installer before you need it.