Six ways to cool a home
Which route fits your situation?
"We're doing a big refurbishment"
Everything is on the table. If your house is semi-detached, terraced or a flat, permitted development allows only one outdoor unit — so the single-unit routes are the shortlist. Detached, or happy to go through planning? The two-unit route joins it.
"We're replacing the boiler with a heat pump — can we add cooling?"
Yes — the easiest win in this guide. As part of the heat pump installation we re-use your existing pipework: UFH cools as it is, and radiators simply swap for fan coils. Full £7,500 grant, least cost and disruption of any route.
"We already have a heat pump — can we add cooling?"
Usually, yes — cooling rides on the system you already own. If the house is heated by underfloor heating, the floor can already add some cooling with no pipe changes at all. In rooms with radiators — or where the UFH sits underneath timber or carpet, floor finishes that don't conduct the cooling well — fan coils replace the radiators, or are added to the room, on the existing pipework. That's option 1 retrofitted; want deeper cooling and room for a second outdoor unit? Add separate AC alongside.
"The boiler's still fine — we just want cooling"
If you'd rather keep the boiler for now, add dedicated air conditioning alongside it — powerful, dehumidifying cooling, though without grant support. And when the boiler does eventually go, the AC carries on working alongside its replacement.
The six approaches in detail
The heat pump's pipework diverts at the tank location into the hot water cylinder, or into one shared circuit — underfloor heating, radiators and fan coils together, no buffer needed.
- One outdoor unit covers heating, hot water and gentle whole-house cooling
- Fan coils heat too — they can top up undersized radiators or replace them entirely
The comfort cooling really makes a huge difference to the downstairs temperature — but not much upstairs, which is all radiators.
A homeowner who retrofitted cooling to her heat pump — UFH downstairs, radiators upstairsThey are a godsend — the lounge with two units in has remained comfortable throughout. The best thing is the bedrooms are cooler at night — nothing worse than trying to get to sleep when you can't cool down.
A homeowner who swapped every radiator for fan coils on this circuit, by email during the June heatwaveComfort cooling keeps the pipe water above the room's dew point (around 19 °C), so it removes heat but not moisture. Rooms drop a very comfortable 5–6 °C — but on a genuinely muggy day the air stays humid: a 25 °C room at 65% humidity cooled to 22 °C sits at about 78%. Cooler, yet slightly close. The water is real, and it has weight: on a muggy day the air inside a typical home is carrying 3–4 litres of water, and genuinely comfortable air means condensing about two litres of it out and throwing it away — work that above-dew-point cooling, by design, never does.
A household of four also adds 5–7 litres of moisture a day indoors — and one load of washing dried on an indoor airer adds roughly two more, so on hot days the washing line earns its keep. Homes with MVHR ventilation track the outside air (~5 affected days a year); without it, moisture builds up (~20 days) — and a small dehumidifier (roughly £25–40 a year to run) clears the lot. Every other route in this guide removes moisture as it cools.
The system here is great — unless the dew point is above, I'd say, 15-ish… so it can't really fight those humid hot days.
The homeowner from the case study below, being honest with usCase study — cooling via UFH
One house, two 35.8 °C days — muggy vs dry
Two days from this house's public monitoring feed — an Econic-installed 12 kW Vaillant Arotherm+ cooling the whole house through the underfloor heating alone. Both days peaked at exactly 35.8 °C outside: one in the muggy late-June heatwave, the other in dry mid-August heat. The gap between the two room lines is what humidity costs comfort cooling.
36 outside, 26 in our hottest room. The feels-like temp is much less though — this inverse radiation, or however you describe it, is great.
The homeowner, messaging us mid-heatwave · 26 June 2026This system publishes its performance openly — view the live data on heatpumpmonitor.org.
Case study — UFH and fan coils on one circuit
UFH downstairs, fan-coil radiators upstairs — one ~20 °C loop
A north-London semi (176 m²) with an Econic-installed Vaillant Arotherm+ — underfloor heating across the ground floor and Jaga fan-assisted radiators in the bedrooms, chosen at design stage to handle heating and cooling alike. In summer one shared loop carries 19–21 °C water to both, day and night: always above the room's dew point, so the floor and the bedroom units cool with no condensation risk anywhere. Same two heatwave days as the case above.
The fan coils did pretty well. We have very large ones in the living room which worked well. The ones in the bedrooms are probably undersized, so struggled to drop the temp but helped to lop the peaks… the house coped pretty well in the extreme with a combination of the shading we installed, the cooling and some active ventilation.
The homeowner, on how the summer wentThe steady-state story is the point: the loop ran quietly around the clock instead of blasting reactively, and 1 kWh of electricity bought 5.5 kWh of cooling across the season. The honest limitation shows here too — on the muggy 38 °C day the rooms crept from 25.0 to 26.2 °C, while the drier 33 °C day was pinned at 23–24 °C throughout. Sizing decides how much each room gets: the generously sized living-room units cooled outright, while the smaller bedroom ones took the edge off the peaks — for a south-facing bedroom or a room in the roof, that's where dedicated AC alongside the heat pump earns its place.
Case study — when comfort cooling isn't enough
The honest counter-example — a bungalow that needs more
A detached bungalow (171 m²) cooling through its underfloor heating — and working genuinely hard at it: 73 cooling days this summer, 2,354 kWh of cooling delivered from 418 kWh of electricity. Yet on the same two hot days as the cases above, the rooms sat far higher. Three things stack against comfort cooling here: the UFH was laid at wide pipe centres, so the floor can only move so much heat; it's a single-storey home, so every room has external surfaces and gains through the roof; and there's little shading on the glass.
The cooling made very little impact with the temperature so high. You could feel the floor was cold but it wasn't making the house feel cold like it does when the heat is on.
The homeowner, by email after the late-May heatThe lesson isn't that the system underperformed — it ran efficiently and flat out. It's that this house's cooling load is simply bigger than a wide-centred floor can absorb. A home like this needs active cooling through fan coils, and would gain more still from cutting the load first — external shading and roof insulation — before any cooling technology is chosen.
One outdoor unit, two circuits: water to the tank and radiator/UFH circuit, refrigerant straight to indoor air-to-air units — capacity time-shared across all three duties.
- When cooling, the heat pulled out of your rooms isn't dumped outside — it's recovered into the hot water cylinder
- Often the best overall technical fit where it's available — for example the Samsung EHS Quint, though it's currently only released in 12 and 16 kW sizes, so it isn't suited to smaller homes yet
- BUS certification isn't expected before January 2027 — we'll confirm at quoting stage
The same start as option 1, but a buffer feeds the fan coils with genuinely cold water — the strongest cooling a heat-pump-led system can deliver, dehumidifying as it goes.
- Needs proper condensate management and a buffer on the cooling circuit
- The chilled water is far too cold for underfloor heating or radiators — they would stream with condensation — so the UFH/radiator circuit stays heating-only and all cooling comes through the fan coils
- The fan coils heat as well as cool — they can replace radiators entirely
- Controls come together in one place: we integrate everything through Heatmiser, so the fan coils, the heating zones and hot water all live in a single app
Case study — active cooling with fan coils
Fan coils pulling a room back on a 34 °C day
23 June 2026, a London townhouse with an Econic-installed 7 kW Vaillant and dedicated fan coils: the room had drifted to 25.6 °C by early afternoon. Chilled water at 8–13 °C pulled it down 4.3 °C in about four hours — still 30+ °C outside — then held it at a steady 21.3 °C through a 27 °C night, draining condensed moisture away as it went.
It's been a revelation… an absolute lifeline this year.
An Econic customer on his living-room fan coil — 21 °C indoors while 35 °C outside — featured in The Guardian, August 2026A split AC unit has refrigerant at around 5 °C inside its coil, so a small box moves a lot of heat. A hydronic fan coil gets 7–12 °C water and delivers roughly half the cooling for the size — Daikin's own catalogue makes the point:
The sizing follows from the size: because hydronic fan coils are physically larger per kilowatt, they're usually sized to just meet the room's peak cooling load — while a traditional AC unit is naturally far oversized for it. So air conditioning can be reactive — switch it on when you're hot and it drags the room down in minutes — while hydronic fan coils are best run continuously, so heat never builds up in the first place. One sprints, the other keeps a steady pace. Part of AC's punch is also invisible: with its coil below the dew point, it spends energy condensing litres of water out of the air — so the room doesn't just read cooler, it feels drier too.
Heating and cooling both come straight from the AC outdoor unit — no radiators or wet pipework anywhere. Hot water is a separate immersion tank (an AC-integrated cylinder exists on some products).
- No gas boiler can remain — the gas system is fully removed, which is also a condition of the expected grant
- Highly disruptive as a retrofit (all wet pipework stripped out); far more straightforward in a new build
- Some products — such as the Daikin Multi+ — combine the AC indoor units with a hot water cylinder on one outdoor unit, but support at most 4 indoor units, so they can't heat and cool more rooms than that
Option 1's heat pump for heating and hot water, plus a completely independent AC system for cooling — two outdoor units sharing no pipework.
- The boiler is fully retired, so this route keeps the £7,500 grant — unlike option 6
- A second outdoor unit is only permitted development on a detached house; anything else needs a full planning application
The gas boiler keeps doing heating and hot water; a separate AC system handles cooling.
- Powerful, reactive cooling — cold air within minutes, dehumidifying as standard
- Doesn't reduce gas use or carbon footprint, and doesn't qualify for grant funding
Heating peaks on winter evenings, when solar panels produce the least. Cooling is the exact opposite: demand rises with the sun. We ran the simulation engine behind our proposals — 17 years of hourly London weather against a 10-panel (4.6 kWp) array and 60 m² of cooled space — and roughly 70% of a summer's cooling electricity is drawn in hours when the panels are generating. And because we only fit solar together with a battery, the midday peak in the chart below isn't wasted — the surplus is stored and carries the cooling on into the evening.
How each system is run compounds this. Reactive air conditioning is often switched on in the evening — when you get home and the house is at its hottest — precisely when solar generation has faded. Hydronic cooling's slow-and-steady style is the better match: running continuously through the day, it removes heat while the sun is paying for it, so the house never reaches the point of needing a hard evening pull-down.
Side-by-side comparison
| Option | Heat source | Hot water | Cooling style | Radiator support | Grant | Disruption & cost | Permitted development |
|---|---|---|---|---|---|---|---|
| 1. Comfort cooling | Heat pump — whole house heating | Heat pump | Light — mostly via UFH, fan coils supplement | Fan coils heat too — supplement or replace radiators | £7,500 BUS | Lowest of the six (as an add-on to a planned heat pump) | 1 outdoor unit |
| 2. Integrated system | Single unit — heat pump + air-to-air | Heat pump | Integrated, time-shared | Depends on system design | Certification earliest Jan 2027 | Medium; cost depends on grant | 1 outdoor unit |
| 3. Active cooling | Heat pump — whole house heating | Heat pump | Active / deep — dehumidifies too | Fan coils heat too — supplement or replace radiators | £7,500 BUS | High — among the most involved | 1 outdoor unit |
| 4. AC-only system | AC unit — heating & cooling, no radiators | AC system (some products) or a separate tank on immersion | Air-to-air — combined heating + cooling | Not applicable — no radiators in this system | ~£2,500 expected | Highest if retrofit; medium if new build | 1 outdoor unit |
| 5. Heat pump + AC | Heat pump — rads & UFH (boiler retired) | Heat pump | Air-to-air — cooling + top-up heating (separate unit) | AC can top up underheated rooms | £7,500 BUS | Medium–high (two installs); medium–high cost | 2 units — detached only |
| 6. Boiler + AC | Gas boiler — rads & UFH (unchanged) | Boiler | Air-to-air — cooling + top-up heating | AC can top up underheated rooms | None | High (cooling) / none (heating); medium–high cost | 1 outdoor unit |
A couple of terms explained
Dew point
The temperature at which moisture in the air starts to condense. Cooling below it removes humidity but produces condensate to manage; cooling above it is gentler and condensation-free.
Boiler Upgrade Scheme (BUS)
The current £7,500 government grant for heat pump installations — amounts and eligibility can change, and not every product is approved yet (the integrated unit, option 2, is awaiting certification). We confirm eligibility at quoting stage.
Air-to-air grant
A smaller grant (~£2,500) expected for air-to-air systems where the gas heating is fully retired. Not live yet — we'll confirm before quoting.
Permitted development (PD)
Under GPDO Class G, most outdoor units need no planning permission provided they also provide heating (cooling-only units don't qualify), stay under 1.5m³, meet noise limits (≤37dB(A) at a neighbour's window) and aren't mounted on a pitched roof. PD allows one unit on most homes, two on a detached house — beyond that, a full planning application. Confirmed at site assessment.
Whichever route you choose: reduce the cooling load
- A dense urban street — hard surfaces soak up heat all day and release it at night
- Large unshaded east-, west- or south-facing glazing, or skylights
- A top-floor flat, absorbing heat through the roof
- A single-aspect flat that can't ventilate front-to-back
- Windows you can't open at night for noise or security
The more of these apply, the more the measures below pay back — and where they can't work at all (a single-aspect flat whose windows stay shut), mechanical cooling is the honest answer.
Risk factors from DECC's "Guidance on preventing overheating in the home".
External shading
Glass is how the heat gets in. External roller blinds, shutters or awnings stop solar gain before it enters — the single biggest lever, and far more effective than internal blinds. South glass is the easy case — a fixed canopy blocks the high summer sun yet admits low winter sun; east and west windows need shutters or blinds.
Night purge ventilation
UK nights stay cool even in heatwaves. A high-flow extract fan running overnight flushes the day's stored heat out of the building fabric before the next morning.
Insulation & airtightness
The winter measures work in summer too: loft insulation keeps roof heat out, and airtightness keeps humid outdoor air from leaking in — most of a muggy day's moisture load arrives that way. Where planning allows, prefer external over internal wall insulation — see below.
Ceiling & floor fans
Moving air feels 2–3 °C cooler than still air at the same temperature — and it pairs beautifully with gentle comfort cooling, spreading the coolness of a cooled floor through the room.
Most period homes we work in can't add external wall insulation — the planners protect the brick façade. So the fabric upgrade that makes winters cheaper and cosier is usually internal wall insulation — and it carries a hidden summer cost: it covers the wall's thermal mass, the very thing that buffers heat on hot days. An internally insulated period home warms up faster and holds its evening heat longer. That doesn't make internal insulation wrong — it makes summer part of the same design decision. If your refurbishment includes internal wall insulation, plan the shading and the cooling at the same time, not after the first heatwave.
A 1930s solid-wall mid-terrace (96 m², no cooling system at all) ran exactly this playbook through summer 2026, with temperature sensors in every main room: 35 °C days outside, 22–24 °C mornings throughout the house. "You can now pretty much sit in any room and feel cool."
and runs quieter — do both
Every property is different — construction, pipework and room usage all shape what's practical and what it costs. The best next step is a site assessment for a property-specific recommendation.
This brief is general guidance and not a quotation. Grant names, rates and eligibility are subject to change by government; actual eligibility is confirmed at quoting stage following a site assessment. Prepared by Econic Energy.