Air conditioning without an outdoor unit
By Airva Editorial Team · Checked against published UK guidance · Updated
Almost everyone searching for this has the same problem: a flat with no balcony, a freeholder who says no, a listed building, or a conservation-area elevation where nothing can go. The honest answer has two halves. There is genuine equipment that works without a separate outdoor unit, and it is worth knowing what it does and does not do. But before you buy it, it is worth being sure the outdoor unit is really impossible — because a conventional split remains substantially better at the job, and "no" is sometimes a first answer rather than a final one.
First, check whether the obstacle is real
Three of the four common blockers are more negotiable than they look.
A freeholder or managing agent refusal. This is a contractual matter, not a physical one. Freeholders routinely consent to a unit on a balcony, a flat roof or a rear light well when asked properly — with a drawing, a noise figure and an undertaking to make good on removal. A blanket "no" to a vague request is not the same as a considered refusal.
Planning permission for a flat. Frequently assumed to be impossible, and it is not. The permitted development right does extend to a block of flats, though only as one installation for the block at 0.6 m³ rather than per leaseholder [1] — so an individual flat usually needs an application. Needing an application is not the same as being refused one. Our flat guide covers the sequence.
A conservation area. The restriction is on elevations fronting a highway [1]. Rear elevations, courtyards and light wells are often compliant.
A listed building. This one is genuinely hard. Permitted development does not apply within the curtilage of a listed building at all [1], and listed building consent is needed for works affecting character. If you are here, the options below are the realistic ones.
The three real alternatives
Through-wall monobloc units
The only genuine fixed air conditioning with no separate outdoor unit. Everything — compressor, coils, fan — sits in one indoor cabinet, with two holes cored through the external wall to draw in and expel air. From outside you see two grilles rather than a condenser.
- Good: properly fixed, permanently plumbed for condensate, far quieter and more efficient than a portable, and visually almost nothing outside. Genuinely the right answer for many listed and conservation-area properties.
- Less good: the compressor is in the room, so it is audible in a way a split is not. Capacity per unit is lower, so it suits one room rather than a house. It needs an external wall with space for two cores.
- Cost: more than a comparable split, because the equipment is specialised and the coring is real work.
Our through-wall air conditioning guide covers the equipment, what the phrase can mean, and honest costs.
Portable units
A box on wheels with a flexible hose out of a window. Universally available, and universally disappointing relative to expectations — but genuinely the right purchase in one situation: a room you need to cool for a few weeks a year.
- Good: no installation, no consent, no permanence. £150–£400.
- Less good: the hose means an open window, which lets warm air back in and fights the machine. Noisy, because the compressor is in the room. Inefficient.
- Worth knowing: movable air conditioning equipment using HFCs with a GWP above 150 is banned in new products [2], so current portables use lower-GWP refrigerants.
See the portable comparison and our round-up of portable units.
Evaporative coolers
Not air conditioning. They pass air over water and cool it by evaporation, which works in dry heat and does very little in a humid British August — and they add moisture to a room that may already feel muggy. Cheap and quiet, and appropriate for a workshop or a garage rather than a bedroom. Set expectations accordingly.
How they compare
| Through-wall monobloc | Portable | Evaporative cooler | Conventional split | |
|---|---|---|---|---|
| Fixed installation | Yes | No | No | Yes |
| Anything outside | Two grilles | Hose out of a window | Nothing | Condenser |
| Noise in the room | Moderate | High | Low | Very low |
| Efficiency | Moderate | Low | Not comparable | High |
| Works in humid weather | Yes | Yes | Poorly | Yes |
| Heats in winter | Many models | Some | No | Yes |
| Typical cost | Higher than a split | £150–£400 | £100–£300 | £1,500–£3,500 |
What you give up, and whether it matters
A conventional split puts the compressor outside. That single decision is why splits are quiet, efficient and capable of cooling a room properly on the hottest day. Every option on this page compromises one of those three, because the compressor has to be somewhere.
For a bedroom you sleep in every night through summer, that compromise is real and you will notice it. For a spare room, a home office used occasionally, or a listed building where the alternative is nothing at all, it is entirely worth making.
Running cost follows efficiency: a less efficient unit delivering the same cooling costs more to run, and our running costs guide shows how to work the figure from the current Ofgem unit rate [3].
Frequently asked questions
Is there real air conditioning with no outdoor unit? Yes — through-wall monobloc units. Everything sits in one indoor cabinet with two cored holes to the outside. It is proper fixed air conditioning, with the compressor in the room rather than outside.
Is a portable unit air conditioning? Technically yes, practically a compromise. The hose requires an open window, which undermines it, and the compressor noise is in the room with you. Fine for occasional use.
Do evaporative coolers work in the UK? Poorly in humid conditions, which describes much of a British summer. They also add moisture to the room. They are not a substitute for air conditioning.
Does a monobloc need planning permission? There is no outdoor unit, but the external grilles are still an alteration to the building — which matters in a conservation area and matters absolutely on a listed building. Check before you core.
Can I get air conditioning in a rented flat? You need the landlord's consent, and the freeholder's above them if it is leasehold. A portable needs neither, which is often why it is the answer in a tenancy.
Are these systems more expensive to run? Generally yes, because they are less efficient than a split delivering the same cooling. That is part of the compromise.
Get an honest answer about your building
The most valuable thing here is finding out whether the outdoor unit is genuinely impossible before you settle for less. Tell us about the property and the constraint and we will match you with one vetted installer who will look at it properly: get an installer match.