A conservatory that hits 38°C by noon in July and feels like a cold garage by October is not a living space. It’s a room you avoid for eight months of the year, which makes it one of the most underused parts of a UK home.
The good news is this is a solved problem. The same technology that cooled your office during the 2026 heatwaves can make your conservatory usable in January and actually comfortable in August. This guide explains why conservatories overheat and get cold, what actually fixes it, and what it costs.
Why your conservatory gets so hot in summer
It’s the greenhouse effect, and your conservatory is doing exactly what a greenhouse is designed to do.
Sunlight passes through the glass and warms the floor, walls, and furniture inside. That heat then gets trapped because glass, especially older polycarbonate or single-pane glazing, provides almost no resistance to heat build-up. On a 25°C day outside, a conservatory with a polycarbonate roof can easily reach 38 to 45°C inside.
The roof is the primary culprit. A conservatory is essentially a glass box. Sunlight passes through the roof and walls, heats the floor and furniture, and because the room is enclosed, that heat has nowhere to go. South-facing conservatories get the worst of it, but east and west-facing ones are not far behind during peak summer.
It also gets worse as the day goes on. The structure absorbs heat all morning and releases it slowly in the afternoon and evening, which is why it often feels hotter at 4pm than at noon even as the sun drops lower.
Why opening windows doesn’t fix it
Ventilation helps, but it has a real limit in a glass-roofed room.
Warm air rises and the hottest air sits right under the roof, exactly where you can’t easily vent it if your only openings are side windows and doors. If your ventilation is mostly at low level, you’ll get some airflow, but the heat cap under the roof can remain. Cross-ventilation is also often restricted by the conservatory’s layout relative to the rest of the house.
Once outside temperatures exceed around 28 to 30°C, which happened regularly during the 2026 summer in the North West, ventilation stops being effective at all. You’re just letting hot air in from outside faster.
Why your conservatory is freezing in winter
The same lack of insulation that causes summer overheating works against you in winter. Glass and polycarbonate have very poor thermal resistance compared to a solid wall. Heat escapes rapidly through the roof and glazing the moment outdoor temperatures drop.
A conservatory built to Building Regulations standards before 2002 can have a roof U-value as poor as 5.8 W/m²K. A well-insulated modern room wall achieves around 0.18 W/m²K. That difference explains why a conservatory feels bitterly cold in October while the room next to it feels fine.
If your conservatory is freezing in October and November, that’s not normal in the sense that it’s unavoidable. It’s normal in the sense that it’s very common with older glazing, and the fix is either improved insulation, active heating, or both. A conservatory that’s genuinely too cold to use in autumn is not reaching its potential as a room.
Can you actually put air conditioning in a conservatory?
Yes, and it works well when it’s correctly specified for the space.
The key difference from a standard room is sizing. A conservatory needs a more powerful unit than a conventional room of the same floor area because glass has far less insulating value than a solid wall. Sizing rule of thumb: allow 0.1 to 0.15 kW per square metre for a well-insulated room, then add capacity for south-facing rooms, large windows, and conservatories.
In practice, most conservatories need a unit in the 2.5 to 5 kW range. A 15 square metre south-facing conservatory with a polycarbonate roof typically needs a 3.5 to 5 kW unit to cope with peak summer heat load. An undersized unit will run at full capacity all day and still not hold a comfortable temperature. That’s why getting the sizing right matters more in a conservatory than in any other room in the house.
Will air con work properly with all that glass, or will it constantly struggle?
A correctly sized wall-mounted split system will hold a conservatory at a comfortable temperature even on a 35°C day. That’s the key qualifier: correctly sized.
An undersized unit will struggle. A portable unit almost certainly will, since portable units have much lower efficiency ratings and vent some warm air back into the room through gaps around the hose. For a conservatory specifically, a wall-mounted split system is the only type worth considering as a permanent solution.
The glass roof and walls don’t prevent AC from working. They simply mean you need more cooling capacity than you’d expect for the floor area. A proper engineer survey accounts for the room’s orientation, glazing type, and solar gain before recommending a unit. Without that survey, any quote is essentially a guess.
It’s also worth noting that a properly specified unit removes humidity as well as heat. That muggy, airless feeling in a conservatory on a hot day comes partly from elevated humidity, not just temperature. A split system handles both simultaneously, which is why a room that was previously unbearable can feel genuinely pleasant within 30 minutes of the unit running.
How much does it cost to install air conditioning in a conservatory?
For a conservatory specifically, expect to pay slightly more than for a standard bedroom installation because of the higher-output unit required.
| Conservatory size | Recommended output | Typical installed cost 2026 |
|---|---|---|
| Small (up to 12m²) | 2.5 kW | £1,500 – £2,200 |
| Medium (12 – 20m²) | 3.5 kW | £1,800 – £2,800 |
| Large (20 – 30m²) | 5 kW | £2,200 – £3,500 |
| Very large or south-facing (30m²+) | 5 – 7 kW or multi-split | £3,000 – £5,000+ |
Prices are based on UK domestic air conditioning costs in 2026 from F-Gas certified installers, updated June 2026. Costs include the unit, labour, pipework, and commissioning. They do not include electrical upgrades if your consumer unit needs additional capacity.
Note that 0% VAT currently applies to residential air-to-air heat pump installations until 31 March 2027, which reduces the effective cost compared to the figures above if you act before that date.
Will it add value to my house?
Increasingly, yes. Air conditioning was considered a luxury addition five years ago. After the summer of 2025 and 2026, it is moving into the same category as a good central heating system in the minds of buyers.
A conservatory with year-round comfort, documented as usable in both summer and winter, is a more convincing selling point than one a buyer knows they’ll have to heat with plug-in radiators and avoid in July. That’s a qualitative value rather than a simple percentage uplift, but estate agents across Warrington and Cheshire are consistently reporting that a functioning, usable conservatory helps rather than hinders a sale.
Where does the external unit go if the conservatory is against the fence?
This is one of the most common practical questions about conservatory installations, and it has workable answers.
The outdoor condenser unit needs adequate clearance on all sides for airflow, typically at least 300mm. It must also meet permitted development rules: the outdoor condenser is Permitted Development in 2026 if it is under 0.6m³ in volume, at least 1m from the property boundary, not installed on a wall or roof facing a highway above the ground floor, and the property is not listed or in a conservation area.
If the conservatory runs right to the fence, the options are:
- Mount the condenser on the house wall adjacent to the conservatory, with pipework running through the conservatory wall to the indoor unit.
- Mount it on a flat roof section if available, provided it meets the 1m setback from the roof edge.
- Position it at the front or side of the property where there’s more clearance, with a longer pipe run to the indoor unit.
A longer pipe run adds a modest cost but doesn’t affect performance if installed correctly. An experienced installer will find the right solution during the survey rather than telling you it can’t be done.
Do I need planning permission?
In most cases, no. Many domestic air conditioning systems may fall under permitted development, provided the outdoor unit meets rules around size, placement, noise, and property type.
The exceptions are listed buildings, properties in designated conservation areas in parts of Chester, parts of the Cheshire countryside, and certain areas of Liverpool city centre, and flats where freeholder or management company consent is also required. If you’re in Warrington, most residential properties in WA postcodes fall under standard permitted development without issue.
From May 2026, the noise standard tightened to 37 dB LAeq at the nearest neighbour’s window, down from 42 dB previously. Modern inverter-driven units from Daikin, Mitsubishi Electric, and LG comfortably meet this standard when correctly positioned. A reputable installer checks noise compliance as standard.
Can the same unit heat the conservatory in winter?
Yes, and this is where the economics of the investment become much more compelling.
A wall-mounted split system runs in reverse as a heat pump in winter. For every unit of electricity it uses, it delivers 3 to 4 units of heat. Compare that to a plug-in electric radiator or oil-filled heater, which delivers 1 unit of heat per unit of electricity at a significantly higher running cost per hour.
| Heating method | Efficiency | Typical running cost per hour | Usable in summer? |
|---|---|---|---|
| Air-to-air split system (heat pump mode) | COP 3.0 – 4.0 | 10p – 20p | Yes, cools in summer |
| Oil-filled electric radiator | 1:1 (100%) | 27p – 40p | No |
| Electric panel heater | 1:1 (100%) | 27p – 40p | No |
| Portable AC unit | Low (SEER 2-4) | 50p – 75p (cooling only) | Yes, but inefficiently |
Running cost figures based on UK electricity rate of 27p/kWh (Q3 2026). Actual costs vary by unit specification and usage pattern.
A split system keeps your conservatory warm in December and January at a fraction of what plug-in electric heating costs. That transforms the economics of the investment from a summer-only purchase into a year-round appliance that earns its keep every month.
Does it help with conservatory humidity and mould?
Yes, and this is an underappreciated benefit. As part of the cooling and heating process, a split system removes moisture from the air. Conservatories are prone to condensation, particularly in autumn and winter when the glass cools rapidly overnight. High humidity also encourages mould on window frames, blinds, and soft furnishings.
Running the unit in dehumidify mode in the cooler months, independent of any heating or cooling function, actively reduces the moisture level in the room. Customers who’ve installed a unit in their conservatory commonly report that the condensation problem they’d had for years largely disappears within one winter season.
Are there any grants available for conservatory air conditioning in 2026?
Not directly. There is no specific grant scheme for conservatory air conditioning. However, two things are worth knowing.
First, 0% VAT currently applies to residential air-to-air heat pump installations, which includes wall-mounted split systems, until 31 March 2027. This is applied automatically by your installer at no extra step from you. On a £2,500 conservatory installation, that’s £125 you’re not paying compared to a standard VAT rate.
Second, if you’re also considering replacing your gas boiler, the Boiler Upgrade Scheme provides £7,500 towards an air-to-water heat pump. That’s a separate system from conservatory AC, but both can run alongside each other and Aquila installs both.
Is a portable unit good enough for a conservatory?
Honestly, no, not for anything beyond a very small conservatory on a mild day.
Portable units have low efficiency ratings (SEER 2 to 4 compared to SEER 6 to 9 for a wall-mounted split), cost around 50 to 75 pence per hour to run, and vent some warm air back into the room through the gap around the exhaust hose. In a glass-roofed conservatory with high solar gain, a portable unit will typically struggle to maintain a comfortable temperature on any day above 25°C outside.
They work as a short-term stopgap. For a room you actually want to use comfortably through summer, they’re not the answer.
Can I install AC myself or does it need to be a certified engineer?
It legally needs to be carried out by an F-Gas registered engineer. Air conditioning systems contain refrigerants that are controlled substances under UK F-Gas regulations. Handling refrigerants without the appropriate certification is illegal. It also voids the manufacturer warranty on the unit itself.
Pre-charged “DIY” split systems are available but they come with limited options, shorter warranties, and cannot be properly commissioned or tested by the installer. They’re not a route we’d recommend for a conservatory installation where correct sizing and commissioning make a significant difference to performance.
How Aquila can help
We install air conditioning and air-to-air heat pump systems in conservatories across Warrington, Cheshire, Liverpool and Greater Manchester. Our engineers are F-Gas certified and experienced with the specific sizing and placement challenges that conservatories present.
Every installation starts with a free survey. We’ll assess your conservatory’s size, orientation, glazing type, and the best position for both the indoor and outdoor unit before recommending anything. If you’re worried about where the external unit can go or whether your conservatory meets permitted development criteria, we check both as standard. No assumptions, no generic quotes built for someone else’s room.
If you’re also thinking about whether air conditioning is worth it for your home more broadly, or you’ve been caught in the debate between a heat pump and air conditioning, our other guides cover both in detail. The conservatory question is usually the clearest case for a split system of any room in the house.
Get a free conservatory air conditioning survey
We cover Warrington, Cheshire, Liverpool and Greater Manchester. We’ll size the system correctly, check planning compliance, and give you a costed proposal with no pressure to go ahead.
Book your free survey at aquila-plumbing.com → or call 01925 234 450
Frequently asked questions
Can you put air conditioning in a conservatory?
Yes. A wall-mounted split system works well in a conservatory, provided it is correctly sized for the higher heat load that glass creates. A conservatory typically needs a more powerful unit than a standard room of the same floor area, usually between 2.5 kW and 5 kW depending on size, orientation, and glazing type.
An F-Gas certified engineer will calculate the right output during a survey before recommending a unit.
Why does my conservatory get hotter than outside in summer?
Because it works exactly like a greenhouse. Sunlight passes through the glass, warms the surfaces inside, and the heat gets trapped because glass provides almost no resistance to heat build-up. On a 25°C day outside, a conservatory with an old polycarbonate roof can reach 38 to 45°C inside.
The roof drives most of the problem. South-facing conservatories suffer most, but any orientation overheats badly during a UK heatwave.
What size air conditioning unit do I need for a conservatory?
As a rough guide, allow 0.15 to 0.2 kW per square metre, compared to 0.1 kW for a well-insulated room. A 15 square metre conservatory typically needs a 2.5 to 3.5 kW unit. South-facing rooms or those with polycarbonate roofs need the higher end of that range.
The only accurate way to size a unit is a heat load calculation by an engineer who has assessed the room in person.
Does conservatory air conditioning help with humidity and mould?
Yes. As part of the cooling process, a split system removes moisture from the air. This directly reduces the condensation and mould that commonly appear on conservatory glass and frames in autumn and winter.
Running the unit in dehumidify mode in cooler months, even without active heating or cooling, makes a significant difference to air quality and surface condensation.
Can air conditioning heat a conservatory in winter, and is it efficient?
Yes, and it’s considerably more efficient than plug-in electric heating. A wall-mounted split system runs as a heat pump in winter, delivering 3 to 4 units of heat for every 1 unit of electricity. A plug-in electric radiator delivers 1 unit of heat per unit of electricity.
In practice, running an air-to-air system in a conservatory through winter costs around 10 to 20 pence per hour, compared to 27 to 40 pence per hour for a standard electric heater of similar output.