The short answer
A conservatory needs more cooling capacity per square metre than an ordinary room because its large glazed area lets in huge solar gain. The rough 0.1–0.15 kW per m² starting point should be revised upward — a sunny, south-facing conservatory can need well above that. A correctly-sized inverter split that both cools in summer and heats in winter is usually the practical answer, but the capacity must come from a proper heat-load calculation, not a floor-area estimate.
A conservatory is the most demanding room in the house to make comfortable: mostly glass, often south-facing, it can become unbearably hot in summer and cold in winter. Air conditioning — specifically a reversible split that heats and cools — is one of the few systems that tackles both. This guide explains why the heat load is so high, how that changes sizing, and what an installer assesses.
Conservatory cooling at a glance
- Main challenge Very high solar gain through glazing
- Sizing Above the usual per-m² rule
- Best type Reversible inverter split (heats & cools)
- Also helps Blinds and solar-control glass cut the load
- Decided by A proper heat-load calculation
- Bonus Same unit warms it in winter
Why conservatories are so hard to cool
A conservatory is essentially a glass box, and glass is poor at keeping heat out. On a sunny day, solar gain pours in through the roof and walls and the space heats up far faster than a conventional room of the same floor area. That is why the usual rough guide of 0.1–0.15 kW per m² understates a conservatory’s needs — the heat load per square metre is simply higher. Orientation matters enormously: a south- or west-facing conservatory bakes in the afternoon, while a north-facing one is more manageable but still glass-heavy.
What pushes the load up — and what brings it down
- Glazed area and orientation — more glass and a sunnier aspect mean a bigger load.
- Roof type — a fully glazed or polycarbonate roof gains far more heat than a solid or insulated one.
- Glass specification — solar-control or low-emissivity glazing reduces gain noticeably.
- Shading — blinds, external shading or planting cut the peak load and let a smaller unit cope.
Reducing the load before you size the unit is worth doing: fitting blinds or solar-control film can mean a smaller, cheaper-to-run system does the job. The cooling still has to overcome whatever gain remains, so the survey must measure the real glazing, not assume a typical room.
| Factor | Effect on cooling load |
|---|---|
| South/west aspect | Much higher — afternoon solar gain |
| Glazed roof | Higher — large overhead gain |
| Solar-control glass | Lower — rejects some solar heat |
| Blinds / shading | Lower — cuts the peak load |
Choosing the right system
A reversible inverter split is usually the best fit because it solves both of a conservatory’s problems: it cools the summer heat and, running as a heat pump, warms the room efficiently in winter when a conservatory is otherwise too cold to use — see heating and cooling air con. Because the load is high, the unit will be larger (and the indoor head bigger) than for an equivalent-sized ordinary room. A portable will struggle to keep up with the solar gain in a glazed space and is rarely a satisfactory long-term answer here.
Sizing and installation
Given the high and variable load, the capacity figure must come from a heat-load calculation that accounts for the glazed area, orientation, roof type and any shading — not a floor-area shortcut. The installer will also plan where the indoor unit and pipework run, since conservatories often have limited solid wall to mount on. As with any refrigerant system, installation is legally restricted to an F-Gas-certified engineer. This page is general information and not a site-specific survey; a qualified installer should confirm the right capacity and unit for your conservatory.
Mounting in a mostly-glass room
Conservatories pose a practical problem that ordinary rooms do not: there is often very little solid wall to mount an indoor unit on. Most of the perimeter is glass and frame, so the installer has to find a structurally suitable spot — commonly the “dwarf” brick wall, the section of house wall the conservatory adjoins, or occasionally a ceiling-mounted cassette where the roof structure allows. The location matters for performance too: the unit needs clear airflow across the room and should not blow straight onto seating. The refrigerant pipework and condensate drain then have to be routed discreetly back to the outdoor condenser, which is one reason a survey is essential before any quote is firm.
It is also worth deciding early whether you want the system mainly for summer cooling, mainly for winter heating, or genuinely both, because that affects sizing and unit choice. A conservatory is one of the strongest cases for a reversible unit precisely because it is uncomfortable at both ends of the year; specifying for both modes from the outset avoids buying a unit that cools well but cannot quite keep the room warm on the coldest days. For the heating side, see heating and cooling air con and check the SCOP as well as the SEER.
Want a conservatory that is usable all year?
An installer can calculate the true heat load of your glazed room and recommend a reversible unit that cools it in summer and heats it in winter. A survey is essential for a room this demanding.
Frequently asked questions
Why does a conservatory need more cooling than other rooms?
Because it is mostly glass, a conservatory lets in a great deal of solar heat, so its cooling load per square metre is much higher than an ordinary room. South- and west-facing conservatories are the most demanding.
What size air con does a conservatory need?
More than the rough 0.1–0.15 kW per m² rule suggests, because of the high solar gain. The exact figure must come from a heat-load calculation that accounts for the glazing, orientation and roof type.
Can air conditioning heat a conservatory in winter?
Yes — a reversible inverter split runs as a heat pump in winter, warming the conservatory efficiently so it is usable year-round. Check the heating efficiency (SCOP) as well as the cooling rating.
Will a portable air conditioner cool a conservatory?
Usually not well. The high solar gain in a glazed room tends to overwhelm a portable’s limited capacity, so a correctly-sized fixed split is the practical choice for a conservatory.
Sources & further reading
- Energy Saving Trust — home cooling and air conditioning guidance
- GOV.UK — Approved Document L (conservation of fuel and power)
- Daikin — capacity and heat-load technical data (used as factual specification)
- Mitsubishi Electric — capacity and heat-load technical data (used as factual specification)
This guide is general information, not a site-specific survey or a substitute for a quote from an F-Gas-certified installer. Installation, servicing and refrigerant handling are legally restricted to F-Gas-certified engineers.