The short answer
A split system is joined into a sealed refrigerant circuit on site, and in Great Britain anyone doing that work needs the right F-gas qualification, with the business holding a company F-gas certificate. Poor work can cause leaks, damage and safety problems.
On this page
A wall-mounted air conditioner can look like a simple fixing job: two units, a hole and some pipes. The skilled part is hidden once the covers are on, and that's where both the legal requirements and most of the risks lie.
The law on refrigerant work
In Great Britain, anyone installing, servicing or dismantling equipment that contains F-gas refrigerants needs the right F-gas qualification. A business doing the work also needs a company F-gas certificate from a certification body. Northern Ireland follows different F-gas rules, which also require qualified engineers.
Split systems are connected into a sealed refrigerant circuit on site, so they are not DIY work. That includes kits sold with pre-filled pipes that connect without special tools.
Refrigerant must never be released into the air. When a system is removed, a qualified engineer recovers the refrigerant, as explained in removing and disposing of an old system. The rules that affect you as a homeowner are in F-gas rules for homeowners.
What the skilled work involves
The steps that need training and specialist equipment are mostly ones you can't check afterwards.
| Step | Why it matters |
|---|---|
| Making flare or brazed joints | Badly made joints leak |
| Pressure testing with nitrogen | Finds leaks before refrigerant goes in |
| Drawing a vacuum on the pipes | Removes air and moisture that cause damage |
| Releasing or adding refrigerant | Gets the charge right with none escaping |
| Recording the work | Shows what's in the system and how it was tested |
Home systems commonly use R32, which is mildly flammable (safety class A2L) and has a global warming potential of 675. It needs handling with the right procedures and equipment, both for safety and to keep it out of the atmosphere. How the pipes are joined and tested is covered in refrigerant pipework explained.
What goes wrong with poor installation
| Shortcut | What can happen |
|---|---|
| Rushed or skipped vacuum | Moisture damages parts over time |
| Poorly made joints | Slow leaks and falling performance |
| Wrong refrigerant charge | Weak cooling and heating, wasted electricity |
| Kinked or crushed pipes | Restricted flow and strain on the system |
| Drain without enough fall | Water dripping indoors |
| Weak fixings or no anti-vibration mounts | Noise, vibration, a unit working loose |
| Unsafe electrical work | Shock and fire risk |
Many of these don't show on installation day. A system can cool well at first and then lose performance as a slow leak takes hold, or develop a fault months later because moisture was left inside.
Warranties and paperwork
Manufacturers' warranties often depend on the system being installed by a suitably qualified engineer, following the installation instructions. A DIY or unqualified installation can leave you without that cover.
A qualified installer also deals with the work around the refrigerant circuit:
- the electrical circuit, which in England and Wales is notifiable under Part P of the Building Regulations
- in England, the MCS 020(a) noise calculation needed for permitted development, with a copy for you
- a commissioning record showing the tests and the amount of refrigerant in the system
- a label on the system showing the refrigerant type and amount
Those documents matter later, for servicing, for warranty claims and when you sell your home.
Checking an installer
Before you accept a quote, ask:
- to see the company's F-gas certificate, and whether the engineers doing the work hold F-gas qualifications
- who will do the electrical work, and whether they're registered with a competent person scheme
- whether you'll receive the noise calculation, commissioning record and certificates
- what the workmanship guarantee covers, and who registers the manufacturer's warranty
A good installer will be happy to answer all of these. More questions worth asking are in questions to ask an installer.
Related guides
- F-gas rules for homeownersF-gas rules in Great Britain require anyone installing, servicing or removing a split system to hold the right qualification, and ban releasing refrigerant. A typical home system is well below the size that needs mandatory leak checks.
- Questions to ask an installerAsk how they sized the system, where both units and the pipes will go, whether it meets planning and noise rules, what the quote includes, which F-gas and electrical qualifications they hold, and what warranty and servicing come with it.
- Refrigerant pipework explainedTwo insulated copper pipes carry refrigerant between the indoor and outdoor units. They are joined at each unit, tested for leaks and cleared of air before use, and their length and route affect how the job looks and whether extra refrigerant is needed.
- Removing and disposing of an old systemAn old split system has to be taken out by a qualified engineer, who recovers the refrigerant before anything is disconnected. The units then go for recycling as electrical waste, and the holes and fixings left behind need making good.