The short answer
A standard split system is installed by mounting an indoor unit on an internal wall, fixing the outdoor condenser outside, and connecting the two with insulated copper refrigerant pipes, a condensate drain and electrical cabling through a small core-drilled hole. The refrigerant circuit must then be pressure-tested, vacuumed and commissioned by an F-Gas-certified engineer — that final step is legally restricted and cannot be done by an untrained person.
A split air conditioning installation looks simple from the outside — one box indoors, one box outdoors — but the work behind it is regulated, sequenced and safety-critical. This guide walks through what a competent installer does, in order, so you know what you are paying for and where the law draws the line. It is general information, not a site-specific survey or a substitute for a quote from an F-Gas-certified installer.
Installation at a glance
- Typical duration Half a day to two days per system
- Who installs it F-Gas-certified engineer (registered company)
- Core hole Roughly 50–65 mm through the wall
- Single split cost £1,500–£3,000 typical 2026 range
- Refrigerant work Legally restricted — certification required
The survey comes first
Before any drilling, a competent installer carries out a survey. They confirm the heat load of the room (the cooling capacity needed in kW), where the indoor unit can sit for good air distribution, where the outdoor unit can be fixed with adequate airflow and access, and the cleanest route for the pipework between them. They also check the electrical supply, because a dedicated circuit is usually required, and look at planning and siting constraints. If the survey is skipped, you risk an undersized unit that runs flat out, or a condenser crammed into a spot where it cannot breathe and so loses efficiency.
Sizing in particular sets up the whole installation. An oversized unit short-cycles and dehumidifies poorly, while an undersized one never reaches setpoint and runs constantly. A good survey also flags the small details that derail an install day — a wall too thin to core safely, a meter board with no spare capacity, or an outdoor position that breaches permitted development. If you are unsure what capacity you need, read what size air con do I need.
The physical install, step by step
Once the design is agreed, the practical work follows a consistent sequence that an experienced two-person team can complete quickly:
- Mount the indoor unit. A back-plate is levelled and fixed to the wall, and the unit is hung on it, typically high on the wall for even air throw across the room.
- Core-drill the wall. A single hole of roughly 50–65 mm is drilled with a slight outward fall so condensate drains away from the building rather than back inside.
- Fix the outdoor condenser. It sits on wall brackets, a ground stand or a flat roof, level and clear of obstructions so it can reject heat freely.
- Run the services. Insulated copper refrigerant pipes (the liquid and gas lines), a condensate drain and the interconnecting electrical cable are run through the core hole and dressed in trunking.
- Make the connections. Pipes are flared and torqued to the manufacturer’s figures; electrical connections are made to a dedicated, isolated circuit.
Up to this point an owner could, in principle, do much of the bracketing and trunking. What follows cannot be done without certification.
Commissioning: the legally restricted part
This is where the job stops being joinery and becomes regulated refrigeration work. The engineer pressure-tests the pipework to prove there are no leaks, then evacuates the circuit with a vacuum pump to remove air and moisture — moisture inside a refrigerant circuit forms acids and causes early compressor failure. Only then is the factory refrigerant charge released from the outdoor unit, or additional refrigerant added for longer pipe runs. The system is started, operating pressures and temperatures are checked against the design, and the controls are configured and demonstrated to you.
What a good installation should leave behind
| Stage | What you should get |
|---|---|
| Survey | Heat-load sizing and a written, site-specific quote |
| Electrical | Dedicated circuit, Part P notification where required |
| Refrigerant | Leak test, vacuum and a commissioning record |
| Handover | Controls demo, warranty paperwork, service advice |
A tidy install also means trunking that follows clean lines, a condensate route that actually drains, and an outdoor unit positioned with planning and noise in mind. For where the outdoor box can legally and sensibly go, see where to position air con units and do you need planning permission.
How long it takes and what it costs
A single-room split is commonly fitted in half a day to a day; a multi-split serving several rooms can take two days or more because of the extra pipe runs and commissioning checks. Typical 2026 UK pricing is around £1,500–£3,000 installed for a single split and £3,000–£6,000+ for multi-split, depending on capacity, pipe length and access. Always get the quote from a certified installer who surveys the property first — a price given without seeing the site is a guess, not a quote, and it usually unravels on the day when reality differs from the assumptions.
Planning an installation?
Use a survey from an F-Gas-certified installer to size the system, agree the pipe route and confirm the electrical and planning position before any work starts.
Frequently asked questions
Can I install air conditioning myself?
You can mount brackets and run trunking, but you cannot legally charge, connect or commission the refrigerant circuit unless you are F-Gas certified. That restriction makes a full DIY split installation illegal in practice.
How big is the hole through the wall?
A single core hole of roughly 50–65 mm carries the refrigerant pipes, condensate drain and cable. It is drilled with a slight outward fall so water cannot run back inside.
How long does a single split take to install?
Most single-room splits are completed in half a day to a full day, assuming good access and a straightforward pipe route between the indoor and outdoor units.
Do I need a separate electrical circuit?
Usually yes. Air conditioning is normally wired to a dedicated, isolated circuit, and that electrical work is notifiable under Part P of the Building Regulations.
Sources & further reading
- gov.uk — Fluorinated Greenhouse Gases Regulations 2015 (GB F-gas)
- gov.uk — Building Regulations: Approved Document P (electrical safety)
- Planning Portal — air source heat pumps and outdoor units
- REFCOM — F-Gas registered company and engineer requirements
This guide is general information, not a site-specific survey or a substitute for a quote from an F-Gas-certified installer. Installation, servicing and refrigerant handling are legally restricted to F-Gas-certified engineers.