Air Conditioning Without an Outdoor Unit UK 2026
You can get fixed air conditioning without a visible outdoor unit in three main ways — a self-contained monobloc wall unit, an internal water-cooled system, or a ducted system with the condenser hidden away — with installed costs ranging from about £1,800 to £8,000+ per room in 2026. This guide explains how each option works, what it costs and which suits a flat, a listed building or a conservation area where an external box is not allowed.
Can you get air conditioning without an outdoor unit?
Yes. There are three practical routes to air conditioning with no visible outdoor unit: a monobloc (all-in-one) wall unit that vents through two small holes cored in the wall (roughly £1,800–£3,000 installed per room); an internal water-cooled system that rejects heat to a water feed and drain instead of an outside box (around £3,500–£6,000); and a concealed or ducted system with the condenser tucked into a loft or cupboard behind discreet grilles (£4,000–£8,000+). Monobloc units are the cheapest and simplest but are less powerful and a little noisier than a conventional split; water-cooled and ducted systems cost more but cool as well as a standard system while keeping the outside of the building untouched.
| Option | How it works | Typical installed cost (per room, 2026) |
|---|---|---|
| Monobloc / all-in-one wall unit | Self-contained unit; two small holes cored through the wall — no external box | £1,800–£3,000 |
| Internal water-cooled system | Heat is rejected to a water supply and drain; nothing mounted outside | £3,500–£6,000 |
| Concealed / ducted (hidden condenser) | Condenser hidden in a loft or cupboard, discreet exterior grilles only | £4,000–£8,000+ |
| Portable unit (temporary, not fixed) | Plug-in unit with a window exhaust hose — no installation, but noisy | £300–£700 to buy |
Supplied-and-installed prices including VAT where applicable, based on UK installer quote data gathered in 2026. London and the South East, including Surrey, typically sit toward the top of each range. Always compare at least three quotes.
Three ways to skip the outdoor unit
Every fixed air conditioner has to move heat out of the room somehow. Without a wall-mounted external condenser, that heat is either blown out through the wall, carried away in water, or vented from a hidden unit. Here is how the three routes compare.
| Option | Best for | Cooling power | Trade-offs |
|---|---|---|---|
| Monobloc wall unit | Flats, extensions and single rooms where no external box is allowed | Good for one small–medium room | Lower output and a little noisier than a split; two vent grilles outside |
| Water-cooled internal system | Listed buildings, conservation areas, upper-floor flats | As strong as a conventional split | Needs a mains water feed and drain; higher install cost and some water use |
| Concealed / ducted | Whole flats or several rooms with a loft, void or cupboard to hide kit | Strong, whole-home capable | Highest cost; needs space to conceal the unit and ductwork |
Indicative comparison only; the right option depends on a site survey. A monobloc still needs two neat core-drilled holes to the outside, so listed-building consent may still apply to the facade.
What drives the price — and who can fit it
As with any air conditioning, the quote depends on the room, the equipment and how much work the install involves. A few things matter more when there is no outdoor unit.
- System type — a monobloc is the cheapest by some margin; water-cooled and concealed ducted systems cost more because there is more equipment and pipework to hide.
- Cooling capacity (kW) — the unit must be sized to the room; a larger or south-facing room needs more output and a higher price.
- Getting heat away — a water-cooled system needs a mains water connection and a drain; a concealed system needs a loft, void or cupboard near an outside wall for the grilles.
- Building fabric — thick or listed walls make core-drilling and routing harder, and may need consent.
- Location — London and the South East, including Surrey, typically run 20–30% above the national average on labour.
On the legal side, it matters which route you choose. A self-contained monobloc is pre-charged and hermetically sealed, so fitting it usually does not involve breaking into the refrigerant circuit — but the electrical connection should still be made by a competent electrician. Water-cooled and split-based ducted systems do contain a refrigerant circuit, so by law they must be installed by an F-Gas certified engineer — that is a legal requirement, not an optional extra, and uncertified refrigerant work is illegal and will void the manufacturer's warranty. Every engineer we match you with is vetted and F-Gas certified. See our guide to F-Gas certification for why it matters.
Choosing an option for a flat or period home
The best choice comes down to your building and how many rooms you want to cool.
If you rent or own a flat where the freeholder or lease bans external units, a monobloc or a water-cooled system usually solves the problem — our air conditioning for a flat cost guide covers the practicalities in detail. In a listed building or conservation area, a water-cooled or concealed system avoids the external box that planners object to, though you should still check whether core-drilling the facade needs consent — see our planning permission guide. If you only need cooling for a few weeks a year and cannot install anything fixed, a plug-in unit may be enough, but it is noisier and less efficient — weigh it up on our portable vs fitted air conditioning page. And if an external unit turns out to be allowed after all, a conventional single split is usually cheaper and quieter than a no-outdoor-unit alternative — compare every route on our installation hub.
What they cost to run
At the Ofgem price cap rate of around 26p per kWh (July–September 2026, a £1,663 cap for a typical dual-fuel home), a small fixed unit costs roughly 18–23p an hour to cool. Monobloc units tend to be a little less efficient than a wall split, and a water-cooled system also uses a small amount of water, so running costs sit slightly higher than an equivalent split.
Most reversible fixed air-to-air systems that also provide heating benefit from 0% VAT until 31 March 2027 under HMRC's energy-saving materials rules; cooling-only units generally do not qualify, so check with your installer. Air-to-air air conditioning is not eligible for the main £7,500 Boiler Upgrade Scheme (which funds air-to-water heat pumps only); a narrower £2,500 air-to-air grant route opened on 28 April 2026 for homes on direct electric heating using an MCS-certified installer and product, so confirm the latest Ofgem criteria before assuming you qualify. Our running costs guide has the full picture.
Frequently asked questions
Sources & methodology
- Installed-price ranges compiled from UK installer quote data gathered during 2026 for monobloc, water-cooled and concealed air conditioning installations.
- Electricity running-cost context from the Ofgem energy price cap, unit rate ~26p/kWh and £1,663 typical annual cap for 1 July–30 September 2026.
- VAT and grant positions from HMRC Notice 708/6 (0% VAT on energy-saving materials to 31 March 2027) and Ofgem Boiler Upgrade Scheme guidance, including the £2,500 air-to-air route from 28 April 2026.
- Prices are supplied-and-installed including VAT where applicable and are indicative, not quotations. Your price depends on a survey.
Get quotes for a no-outdoor-unit system
Air Con Surrey is a free matching service. Tell us about your room and building and we'll match you with vetted, F-Gas certified air conditioning engineers who survey your property and quote for the right no-outdoor-unit option — so you compare real prices, not estimates.