Air conditioning for flats and apartments

Yes, you can have air conditioning in a flat or apartment. What you can install comes down to three things: whether you rent or own, whether you can get your freeholder's permission, and whether there is anywhere to put an outdoor unit. Answer those three and your best option falls out almost by itself. Renters, and anyone who cannot get consent, are best served by a portable unit. Leaseholders who can get permission and have a balcony or a stretch of external wall should fit a reverse-cycle split. Where there is no room for a condenser at all, a monobloc or no-outdoor-unit system fills the gap.

The hard part of apartment air conditioning is rarely the kit. It is permission. So this guide starts with the constraints flat-dwellers actually face, then matches each situation to the right system, with honest UK prices and the planning and noise rules that apply to flats specifically.

Which option fits your situation

The table is the short answer. The rest of this guide explains how to get each one right, starting with the step most people skip.

Start with permission, not the product

In a flat, you rarely own the outside walls, the roof, the balcony structure or the building's appearance. Your freeholder does. That single fact shapes everything, so sort out permission before you fall for a particular unit.

If you rent

You need your landlord's written permission before installing anything fixed to the property. In practice that rules a split system out for most renters, because it means drilling the wall, running pipework and fixing an outdoor condenser to a building you do not own.

The honest answer for renters is a portable unit. It needs no fixing, vents through a window kit and comes with you when you move. It is worth a quick message to your landlord anyway, so there is no argument about a partly-open window or a bracket later.

If you own a leasehold flat (which is most flats)

Owning your flat does not mean you can do as you like to the outside of the building. Almost every lease requires the freeholder's or managing agent's written consent for external alterations, and for any work that touches the structure or the shared parts. That consent is usually formalised in a document called a licence for alterations (a "licence to alter"), which can set conditions on working hours, contractor qualifications, insurance, acoustic treatment and putting things back if you leave.

Crucially, consent can be needed even for a system with no outdoor box. If refrigerant pipework passes through an external wall, if a condenser sits outside, or if condensate drainage runs through communal routes, the managing agent will usually want to approve it. When they review a request, expect to submit the unit's location and size, its noise data, the pipe and drainage routes, and the electrical details.

In a flat, the first question is not which unit to buy. It is who you have to ask.

Read your own lease, because it governs, and be prepared for a "no". Freeholders can and do refuse, often on the look of the building or the risk of noise complaints. The issue is contested enough that there is a live UK Parliament petition calling for freeholders to allow compliant fixed units unless they have a solid reason to refuse. Until anything like that becomes law, treat consent as something to secure first and to have a fallback for. Installing without it puts you in breach of your lease.

Planning permission for a flat is stricter

Planning permission is separate from your freeholder's consent, and you can need both. For flats it is tighter than for houses.

The key distinction is what the unit does. A reverse-cycle unit, which heats as well as cools, can qualify as permitted development in England under rules in force since 29 May 2025. A cooling-only unit is specifically excluded ("not used solely for cooling") and generally needs a full planning application. Even where permitted development applies, the conditions for flats are tighter than for houses: the unit must be no larger than 0.6 cubic metres (houses get 1.5), only one unit is allowed on the block, it cannot sit on a pitched roof or within 1 m of a flat-roof edge, and it cannot go above ground-floor level on a wall facing a highway.

Flats, listed buildings and conservation areas are treated more strictly, and upper-floor siting and appearance rules often knock permitted development out in practice. So for a flat, assume you should check with your local planning authority before committing. If you do need a full householder application, the fee in England is £548 from April 2026. Scotland, Wales and Northern Ireland have their own rules. Our guide to planning permission for air conditioning covers the conditions in detail.

Fees and rules correct as of July 2026. Always confirm with your local planning authority before installing.

Noise and your neighbours

Noise is the objection that sinks the most flat installations, and it is written into the rules. An outdoor unit must not exceed 37 dB(A) measured one metre from the nearest neighbour's habitable-room window or door, under the current MCS assessment. In a dense building with balconies close together, that is a real constraint, and it is exactly what a freeholder is protecting against when they ask for noise data.

Good siting solves most of it: keep the condenser away from bedroom windows, use anti-vibration mounts, and pick a quiet unit. A reputable installer will do the noise assessment as part of the job. If you are going the portable route, be honest that portables are noisier indoors, which matters more in a small flat.

Your options by situation

Renting, or no permission: a portable

A portable air conditioner is the right call if you rent, if your freeholder says no, or if you just want cooling this week without a project. It plugs in, vents hot air out through a window kit, and needs no installation, no F-Gas engineer and no planning permission. For a flat, a 2.0kW unit suits a small bedroom and around 2.9kW suits a larger or open-plan room.

The trade-offs are real: portables are noisier and less efficient than a fixed system, and the window kit means a window that will not fully close. If tidiness matters, look at the newer designs in our guide to the portable air conditioner without a hose. You can compare current models in our portable air conditioners section.

Leaseholder with a balcony or wall: a reverse-cycle split

If you own a leasehold flat, can get consent and have somewhere for the condenser, a wall-mounted reverse-cycle split is the best long-term answer. It is quiet, efficient and permanent, and because it is reverse-cycle it heats the flat in winter too, which is also what lets it qualify for permitted development and, in narrow cases, a grant.

The catch is the outdoor unit. It needs a viable home: a balcony (if your lease permits units there, which many do not), a bracket on an external wall, or a ground or roof position agreed with the freeholder. A single split for one room in a flat typically costs £1,500 to £2,500 fitted, and a multi-split serving two or three rooms £3,000 to £6,000, with flats often at the upper end because access is harder on upper floors. The work must be done by an F-Gas-certified installer, because it involves refrigerant. To weigh a split against the alternatives, see how to choose an air conditioning system.

No room for a condenser: monobloc or no outdoor unit

Plenty of flats have nowhere to put an outdoor box, whether that is a north-facing wall onto a courtyard, a balcony that bans units, or a freeholder who will not allow anything visible. This is where a no-outdoor-unit system earns its place.

There are two routes. A self-contained monobloc wall unit sits inside and exhausts through two small holes cored in an external wall, with no separate condenser. A water-cooled system hides the condensing equipment indoors, in a cupboard or utility space, and rejects heat to the mains water instead of the air. Both avoid the visible outdoor box that stops so many flat installs, at a convenience premium, and a water-cooled system still needs decent mains pressure and, being a refrigerant system, a qualified installer. We cover the trade-offs in full in air conditioning without an outdoor unit.

What it costs to run

Buying and fitting is one cost; running it is another. A portable drawing about 1kW, run for eight hours, uses 8 kWh. At the Ofgem price cap of 26.11p/kWh, that is 8 × £0.2611, or about £2.09 a day. A fixed reverse-cycle split cooling the same room is markedly more efficient, so it costs less per hour to run, which is part of why it earns its higher upfront price over time.

Running-cost figure uses the Ofgem cap for 1 July to 30 September 2026 (26.11p/kWh). The cap changes quarterly, and from 1 October 2026 VAT on domestic electricity is cut from 5% to 0%, so check the current rate before budgeting. For a fuller breakdown, see how much air conditioning costs.

Can you get a grant for a flat?

Only in narrow circumstances. A £2,500 air-to-air grant is available in England and Wales, but it applies to reverse-cycle units that heat as well as cool, fitted by an MCS-certified installer to replace an existing fossil-fuel or electric heating system, and one per property. A flat can qualify in principle, but you would still need your freeholder's consent, so it is not a shortcut around permission. Comfort cooling alongside a boiler you are keeping, and portable units, do not qualify. There is also 0% VAT on qualifying permanently-fixed air-to-air heat pumps until 31 March 2027, which does not apply to portables. This is not "free air con", so check GOV.UK for current availability before you count on it.

Grant and VAT rules correct as of July 2026. Confirm current eligibility on GOV.UK and Ofgem before committing.