How is air conditioning installed?

If you want to know how to install air conditioning in a UK home, the honest answer is that a fixed wall-mounted split is a one-day job for a qualified engineer, not a weekend DIY project. The mechanical part looks simple enough (two units, one hole through the wall, some pipework), but the steps that actually make the system work, pressure-testing, vacuuming and charging the refrigerant, are legally restricted to an F-Gas-certified engineer. Doing them without that certification is a criminal offence.

So this guide does two things. First, it demystifies the install: a clear, numbered walkthrough of exactly what happens on the day, so you know what a fair quote covers and can see it is a low-disruption job. Second, it is straight with you about the law, including where "pre-charged" easy-fit kits really stand. A portable unit is the one type that genuinely needs no installation, and we cover that too.

What actually happens when air conditioning is installed

A single wall-mounted split has two parts joined by refrigerant pipework: an indoor unit (the evaporator) mounted high on a wall inside, and an outdoor condenser unit outside. Insulated copper refrigerant pipes, a control cable and a condensate drain run between them, usually hidden in trunking.

Here is the realistic step-by-step process for a single split in the UK.

1. Survey and siting. Often a separate visit, or a remote photo or video survey. The installer sizes the system for the room using a heat-load (BTU) calculation, not just floor area, then agrees where the indoor and outdoor units go, the pipe route and the drain run. Siting balances performance, pipe length, noise, looks, how close the boundary and neighbours are, and any planning constraints.

2. Mount the indoor unit. A metal mounting plate is fixed and levelled on the wall, and the indoor unit clips onto it. It sits high on the wall with clear space around it for airflow.

3. Drill the wall penetration. A single core hole, roughly 65 to 80 mm, is drilled through the external wall at a slight downward angle, to carry the refrigerant pipes, control cable and condensate drain.

4. Mount the outdoor condenser. The condenser is fixed outside on wall brackets or a raised ground base, on anti-vibration mounts, in a ventilated spot. For a single room it is roughly the size of a small suitcase, around 70 to 80 cm wide.

5. Run the pipework, drain and electrics. The insulated copper pipes, condensate drain hose and cabling are run between the units, usually in trunking. A dedicated, correctly-fused electrical supply and an external isolator are connected. This is notifiable electrical work.

6. Pressure test. The pipework is pressurised with oxygen-free nitrogen and checked for leaks before any refrigerant goes in.

7. Vacuum (evacuation). A vacuum pump removes all the air and moisture from the pipework. This is essential for efficiency and for the system's lifespan.

8. Release the refrigerant. Once the system holds a vacuum, the engineer releases the refrigerant that is pre-stored in the outdoor unit into the lines, topping up for longer pipe runs as needed.

9. Commission and hand over. The engineer runs the system, checks operating pressures, tests cooling and heating, leak-checks the joints, documents the commissioning, registers the warranty and shows you the controls.

Steps 6 to 8 are the heart of the job, and the reason a split is not a DIY install. They are the legally F-Gas-restricted work, explained below.

How long it takes and how disruptive it is

For a single split, the on-site work usually takes about a day once it begins. The disruption is genuinely low: the system is ductless, so the job is mounting two units, drilling one core hole and connecting them. There is some drilling noise and dust, but no major building work.

From first enquiry to a finished install, a managed national installer can run to around two weeks end to end. Almost all of that is lead time and the survey, not time spent on site.

Bear in mind these are typical figures, not guarantees. Difficult access, scaffolding, long pipe runs, hard walls or a multi-room job will all add time.

Can I install air conditioning myself?

For a fixed split, no, not lawfully or sensibly. You could physically mount the two boxes and run the trunking, but you cannot legally make the refrigerant connections, and without the pressure test, vacuum and charge the system will not work properly anyway.

The one exception is a portable air conditioner, which needs no installation. You wheel it in, attach the exhaust hose to a window venting kit and plug it into a standard socket. It is a true plug-and-play option. The trade-off is that portables are noisier and less efficient than a fixed split, so they suit occasional use rather than being a permanent fix.

Why a split legally needs an F-Gas engineer

Modern UK domestic splits run on R32 refrigerant (a lower-impact gas than the older R410A). Under the UK Fluorinated Greenhouse Gases (F-Gas) Regulations, only a certified engineer working for a certified business may install, commission, service or decommission equipment that contains this refrigerant.

In practice that means the engineer holds a personal Level 3 F-Gas qualification (such as City and Guilds 2079 or a BESA equivalent), and the company holds F-Gas certification, for example with REFCOM. Trade bodies are clear that carrying out this work without certification is a criminal offence.

A cheap quote from someone without F-Gas certification is a false economy, and often an illegal one.

This is exactly why steps 6 to 8 above, breaking into the refrigerant circuit to braze or flare the joints, pressure-test with nitrogen, vacuum out the air and moisture, then release the charge, are not a homeowner job. They are not just fiddly; they are regulated.

The pressure test and vacuum are not optional polish, either. The nitrogen pressure test finds leaks before any gas goes in, and the vacuum removes air and moisture that would otherwise wreck efficiency and shorten the system's life. Skipping or rushing the vacuum is one of the most common causes of an air conditioner that underperforms or fails early. The exact pressures and evacuation times vary by manufacturer, which is another reason it belongs with a trained engineer.

Are pre-charged or easy-fit DIY kits legal in the UK?

This is where a lot of DIY content is misleading. "Pre-charged" or "easy-fit" split kits exist, with the refrigerant sealed in the outdoor unit and quick-connect couplings, and they are marketed as something a homeowner can fit. They reduce the on-site refrigerant fiddliness, but they do not lawfully turn you into the installer of the gas circuit.

The F-Gas rules still apply. Non-hermetically-sealed equipment charged with F-gas may only be sold to an end user where there is evidence that a certified business will carry out the installation, and a retailer can refuse the sale if it looks like a way to bypass competent installation. Connecting the refrigerant circuit is the regulated step, full stop.

This is enforced. The Environment Agency has prosecuted online sellers who failed to check their buyers, and in one case an online retailer was fined £37,500 for selling air conditioning units without evidence that a certified installer would fit them. Demand climbs in every heatwave, which is exactly when the riskiest online buying happens, so it pays to know where you stand before you buy.

A simple test when buying online: a responsible retailer selling a split system will ask you to confirm an F-Gas registered installer before it completes the sale. If a site lets you buy a pre-charged split with no questions asked, treat that as a warning sign rather than a bargain.

There are practical downsides too. Self-fitting such a kit typically voids the manufacturer's warranty, may breach your home insurance, risks an illegal refrigerant release, and the electrical work is still notifiable. If a seller claims a kit needs "no F-Gas" or is "self-fit and compliant", treat that with scepticism and check the specific product's refrigerant and compliance before buying.

What about the electrics and planning permission?

The electrical side is notifiable work under the Building Regulations. The dedicated fused supply and the external isolator must be installed or certified by a competent, qualified person (this is the Part P requirement). It is usually quoted separately, and commonly adds £400 to £700.

On planning, the key distinction is whether the unit also heats. The outdoor condenser is treated as an air source heat pump:

• A reverse-cycle unit (one that heats as well as cools) can usually be installed under permitted development on a house, subject to conditions on noise, unit size and siting.

• A cooling-only unit generally needs full planning permission.

Flats, listed buildings and conservation areas typically need consent regardless, and the rules differ in Scotland, Wales and Northern Ireland, so always check with your local planning authority. Our air conditioning planning permission guide covers this in full.

What it costs, in brief

This is an explainer rather than a cost guide, so just the headline: a single split, supplied and fitted, typically costs roughly £1,500 to £3,000 per room, with a typical bedroom job landing around £2,000 to £2,500. Add the notifiable electrics at £400 to £700 if they are quoted separately. Portable units cost roughly £300 to £650 to buy, with no installation cost.

For the full breakdown of what a quote should cover and what moves the price, see our air conditioning cost guide.

Prices and figures were correct at July 2026 and change frequently. Quotes vary from home to home, so always confirm current prices before budgeting.

How to find a qualified installer

Because the refrigerant work is legally restricted, the single most important thing you can check is that the company is F-Gas certified. Ask for their certification and don't be tempted by a quote that undercuts everyone else from someone who can't show it.

You can check a company yourself by searching the REFCOM register by postcode or company name, and a legitimate engineer can show an F-Gas certificate or an ACRIB SKILLcard on request. To skip the legwork, you can compare F-Gas registered installers in our directory and get quotes from companies qualified to do the work.