Air conditioning for a conservatory: does it actually work?
Conservatories are the hardest room in a UK house to cool. Huge glass area, low insulation and a sun-facing aspect mean a standard-size unit will run flat-out and still lose the battle on a hot day. Here's what actually works — and what doesn't — from an installer that fits AC in Midlands conservatories every summer.
Why conservatories are so hard to cool
A typical 3m × 4m lounge needs about 3.5 kW of cooling. The same-sized conservatory can need 6–8 kW because of the greenhouse effect — glass roofs and walls trap solar heat all day. On a 30°C afternoon, a west-facing conservatory can hit 45°C+ without shading.
Sizing — go bigger than you think
| Conservatory size | Cooling capacity needed |
|---|---|
| Up to 12 m² (small lean-to) | 5.0 kW |
| 12 – 18 m² (medium) | 6.0 – 7.1 kW |
| 18 – 25 m² (large) | 7.1 – 9.0 kW |
| 25 m²+ (orangery / open-plan) | 9.0 kW+ or multi-split |
For comparison, a standard lounge unit is 2.5–3.5 kW. Undersize the conservatory and you'll blow the biggest budget item — the outdoor unit — and still be hot.
What you'll pay
- Small conservatory (5 kW single-split): £2,400 – £2,900 fully fitted
- Medium conservatory (7.1 kW): £2,900 – £3,600 fully fitted
- Large / orangery (multi-split or 9 kW): £3,800 – £5,000+
Things that help the AC work harder
- Solar-reflective roof film (£300–£600) — cuts heat gain by 60–80%
- External blinds or awnings on south/west glass
- Insulated conservatory roof panels (a full roof replacement is £4k+ but transforms the space)
- Keeping doors to the house closed on hot days so the AC isn't fighting the whole property
When we tell customers no
If the conservatory has a polycarbonate roof, single glazing and no shading, we'll be honest: even a 9 kW unit will struggle on 32°C days. We'll usually recommend fixing the shading first, then coming back to talk AC. It's not the sale we want — it's the outcome you want.
The winter bonus
The upside of AC in a conservatory is winter. Modern units heat as well as cool, and reclaim the room from October to March at a fraction of extending your central heating. Most conservatory customers end up using it more for winter heating than summer cooling.
FAQ
Can one AC unit cool a whole conservatory?
Yes, provided you size it correctly. For anything over 20 m² or with heavy west-facing glass, we'd usually spec two smaller units on a multi-split instead of one giant one — better airflow coverage.
Where does the indoor unit go?
Usually the solid wall shared with the house, high up so cool air falls across the room. We avoid mounting on glass frames (structural and drainage issues).
Will it work with a polycarbonate roof?
It'll help but won't fully win on the hottest days. Add solar film or insulated roof panels first — the AC then works properly rather than flat-out.
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