Conservatory Cooling: What Actually Works?

Most conservatory cooling UK advice online focuses on blinds, roof vents and fans. Those measures help, but they will not keep a south or west facing glazed conservatory comfortable during a UK heatwave. A properly sized split system air conditioning unit does solve the problem, though conservatory installations carry a few specific considerations around where the units sit, the pipe run, and planning permission that a standard room installation does not.

Why passive measures are not enough for a south-facing conservatory

A glazed conservatory behaves like a solar collector. On a south or west facing aspect, internal temperatures can reach 40°C or higher during sustained UK heatwave conditions. Roof vents, external blinds and standing fans all reduce peak temperature to some degree, but none of them remove heat from the room. They slow the problem down. They do not solve it.

External blinds outperform internal blinds because they block solar gain before it enters the glass, rather than after. Good roof ventilation helps hot air escape rather than pooling at ceiling height. Both are worth doing regardless of whether you install air conditioning, because they reduce the load the AC unit has to work against. But on their own, in a genuine heatwave, they will not bring a conservatory down to a comfortable living temperature.

How a split system AC unit works for a conservatory

A split system indoor unit is mounted on a wall, typically the house wall where the conservatory joins the main property. It cools the conservatory space directly by drawing in warm air, removing heat, and circulating cooled air back into the room. The outdoor condenser sits outside, connected by a pipe run carrying refrigerant between the two units.

For a standard UK conservatory of 15 to 25 square metres, a 2.5kW to 3.5kW unit is typically sufficient, though the correct size depends on aspect, glazing area and construction, not floor area alone. An installer should carry out a proper heat load calculation rather than sizing from square metreage.

Where to position the indoor and outdoor units

The indoor unit goes on the house wall inside the conservatory, not on the conservatory’s own wall or roof structure. The outdoor condenser should be wall-mounted on the main house exterior, or ground-mounted in the garden. It should not be fixed to the conservatory itself.

Conservatory roofs and walls are built to a lighter specification than the main house structure. They are not designed to carry the ongoing vibration or weight of a condenser unit. If an installer proposes mounting the condenser on the conservatory structure, ask them to reconsider the siting before you agree to anything.

The pipe run typically passes through the house wall, connecting the indoor unit inside the conservatory to the outdoor condenser outside on the same wall. This keeps the run short and avoids putting any penetration through the conservatory’s glazing or roof.

Planning permission: what applies to conservatory installations

Conservatories themselves sometimes carry planning conditions from when they were built, occasionally including a condition that no further development takes place. That is separate from the rules governing air conditioning units.

The permitted development rights that apply to home air source heat pump installations under Class G apply to the main dwelling, not to the conservatory as a structure. Where the indoor unit sits on the house wall and the outdoor condenser is wall-mounted on the house or ground-mounted in the garden, as recommended above, the installation is assessed against the standard Class G conditions for the main house.

Those conditions require the unit to provide a heating function, meaning it must be an air-to-air heat pump rather than a cooling-only system, since cooling-only units are excluded from Class G permitted development rights entirely. The outdoor unit’s volume must stay under 1.5 cubic metres for houses, a figure widely misreported elsewhere as 0.6 cubic metres. The property must not be in a conservation area or have listed status, and the unit cannot go on a wall facing a highway.

A fuller breakdown of planning permission rules for AC installations, including edge cases around conservation areas and listed buildings, is planned for a dedicated guide on this site. That page is not yet live, so it is not linked here.

Sizing your unit correctly

Conservatories generally need a larger unit than a standard room of equivalent floor area, because glazing lets in far more solar heat than brick and plaster walls do. A 20 square metre conservatory may need a 3.5kW unit, where a 20 square metre bedroom with normal window proportions might only need 2.5kW.

Floor area alone is not a reliable guide. Aspect, glazing percentage, roof type (polycarbonate versus glass versus solid tiled) and shading all affect the actual cooling load. Ask any installer quoting for a conservatory whether they have carried out a heat load calculation specific to the room, rather than a generic per-square-metre estimate.

What it costs to run

Using the Ofgem electricity unit rate for Q3 2026 of 26.11p per kWh, effective from 1 July 2026, a 3.5kW unit with an EER of 3.5 draws approximately 1kW of electricity per hour of operation. That works out to roughly 26p per hour of running cost. For six hours of afternoon and evening use during heatwave conditions, that is approximately £1.57 per day. These figures are illustrative rather than exact, since real consumption depends on the unit, the thermostat setting and how hard the system is working on any given day.

A full breakdown of running costs across different unit sizes and usage patterns is planned as a separate guide on this site, covering the calculation in more detail. That page is not yet live, so it is not linked here.

Final verdict

If your conservatory is unusable in summer, a properly specified split system AC unit is the solution, not blinds or vents on their own. Keep passive measures in place because they reduce the load and cut running costs, but do not expect them to solve the problem alone. Get quotes from installers who are willing to do a proper heat load calculation rather than sizing from floor area, and be clear with them upfront that the outdoor condenser goes on the house wall or in the garden, not on the conservatory structure. If an installer pushes back on that point, treat it as a reason to get a second quote.

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