Flats can overheat badly. Top floors take the sun on the roof, big windows face one way, and there’s often no way to get a breeze through. Fitting air conditioning is usually possible, but there are more people to ask and fewer places to put things than in a house.
This guide covers lease consent, the planning rules for flats, the options for the outdoor unit, pipe routes and fire stopping, working at height, neighbours and costs.
Start with the lease
Most flats are leasehold, and most leases restrict alterations to the structure and the outside of the building. An outdoor unit on an external wall, a balcony or a roof, and a hole through an outside wall, will usually need the landlord’s written consent, often through a managing agent. Some buildings have their own rules on where units may go.
Ask early, and include photos, a drawing of the proposed positions and the manufacturer’s data sheet. We can provide the technical details from our survey. Our guide to leasehold consent explains the process. This is general information, not legal advice.
Planning rules are different for flats
The Planning Portal’s heat pump guidance sets separate limits for flats and blocks of flats: for example, the outdoor unit can be no more than 0.6 m³, compared with 1.5 m³ on a house. As with houses, permitted development doesn’t cover a unit used only for cooling, and it doesn’t apply to listed buildings. Article 4 directions can remove rights in some areas. Check with the council if you’re unsure.
Where the outdoor unit can go
- A private balcony is often easiest, on the floor on a stand or on a wall bracket. Check the balcony’s structure, drainage and clearances.
- A rear wall bracket on a lower floor or courtyard elevation, where the lease and planning allow.
- A roof or plant area on purpose-built blocks, with consent and safe access for servicing.
- Ground level in a garden or bin store, with a longer pipe run. Each model has a maximum pipe length and height difference, which we check.
Our guide on where to put the outdoor unit covers clearances and airflow.
If there’s nowhere for an outdoor unit
Some flats simply can’t have an outdoor unit. Options then include through-wall units that sit entirely inside the room and use two holes in the wall, which are less efficient and usually louder than a split; and portable units, which are least efficient. Under the GB F-gas bans, new portable air conditioners can’t use HFCs with a GWP above 150. See our comparison of fixed and portable air conditioning.
Want it done properly? AirCon Doctor installs, repairs and services air conditioning and heat pumps across London and the South East, from our base in East Grinstead. We’re an F-Gas certified company and NICEIC approved. Get a fixed-price quote.
Pipe routes, condensate and fire stopping
Inside the flat, pipework runs in neat trunking or is hidden in voids. Condensate needs to fall to a waste with a trap, or be pumped. Where pipework passes through a wall or floor between flats or into a shared corridor, that wall or floor is usually a fire separation. Any hole through it must be properly fire-stopped. We plan routes to avoid these walls where we can.
Working at height
Above the ground floor, fitting and servicing an outdoor unit on a wall needs safe access: a tower, a mobile platform or, on some buildings, roof access. That affects the price and sometimes needs the managing agent’s permission for the equipment. We include access in the fixed-price quote after the survey.
Neighbours above, below and beside
Outdoor units should sit away from neighbours’ windows and balconies, on anti-vibration mounts. Indoor units on party walls can carry noise, so we often choose an outside wall instead. Our noise guide has more.
Costs
A single room split system costs £1,200–£2,200 + VAT; a 2-room multi-split £2,800–£4,500 + VAT. A multi-split is often the best answer in a flat, because one outdoor unit serves several rooms. Access equipment and long pipe runs are priced after the survey.
Quick answers
Do I need permission to fit air conditioning in my flat?
Usually you need the landlord’s consent under your lease, and you should check the planning rules for flats with the council. Listed buildings need listed building consent.
Can the outdoor unit go on my balcony?
Often, yes, subject to your lease, the balcony’s structure and the airflow clearances the manufacturer specifies.
What if my flat can’t have an outdoor unit?
Through-wall units and portable units are options, though less efficient. We can tell you at the survey whether a split is possible.
Is a multi-split good for a flat?
Often. One outdoor unit can serve several rooms, which suits flats with limited outside space.
Related services
- Domestic air conditioning
- Multi-split air conditioning
- Wall-mounted air conditioning
- Air conditioning installation
More advice
- Air Conditioning in a Leasehold Flat: Getting Consent
- Where to Put an Air Conditioning Outdoor Unit
- Air Conditioning vs Portable Air Conditioner: Which Is Better?
- Multi-Split Air Conditioning: Is It Right for Your Home?
- Air Conditioning Noise: How Quiet Are Modern Systems?
- All advice
This guide is general information, checked against the sources linked on 30 October 2026. It isn’t legal, tax or financial advice. Rules, grants and product ranges change, so check the current position before you rely on it.