Search for air conditioning online and you’ll find split systems sold as DIY kits: the outdoor unit arrives already holding refrigerant, the pipework has quick-connect couplings, and the instructions make it look simple. Some kits are marketed as needing no specialist tools.
The trouble is that a split system is not a sealed appliance. Connecting the pipework opens the refrigerant circuit to the rest of the system, and in Great Britain that is regulated work. This guide sets out what GOV.UK says, what it means for you as a buyer and why a properly fitted system is a different product from a DIY one.
What GB F gas law says about installation
GOV.UK’s guidance on qualifications to work on equipment containing F gas says that for refrigeration, air conditioning and heat pump systems you must have qualifications to install new systems, service and maintain them, check for leaks, recover gases and decommission old systems. The guidance does not exempt pre-charged equipment.
Companies doing the work must also be certified. GOV.UK’s company certification guidance says a company, including a sole trader, must be certified by an approved body to install, repair, maintain or decommission F gas equipment. In short: the person connecting the system needs the right F gas qualification, and the business they work for needs F gas certification.
What sellers must do
GOV.UK’s guidance on selling F gas or equipment says that before selling non-hermetically sealed equipment containing F gas to a customer, the seller must ask the end user for the details of the qualified technician who will install it and check those details are valid. The guidance says the seller should get the details in writing. Hermetically sealed equipment, such as a sealed portable unit, is exempt from this step.
A split system with separate indoor and outdoor units joined by pipework is not hermetically sealed. So a seller is expected to know who will install it. If a website sells you a split kit without asking, that doesn’t make DIY installation lawful.
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.
Why it matters beyond the law
- Leaks. Quick-connect couplings can leak if they are cross-threaded, kinked or not tightened correctly. A leak releases a greenhouse gas and leaves you with a system that slowly stops cooling.
- Air and moisture. Professional installs pressure-test and evacuate the pipework before releasing refrigerant. Moisture left in the system can damage components over time.
- Electrics. A fixed system usually needs a dedicated circuit, which in a home in England is notifiable under Part P. See new circuits and Part P.
- Warranty. Manufacturers’ warranty terms often depend on correct installation and commissioning. Check the terms before you buy.
- Future repairs. Engineers need to know what has been done to a system. Without commissioning records and F gas paperwork, diagnosis is harder.
VAT on kits bought online
HMRC’s Notice 708/6 zero-rates the installation of qualifying heat pumps in homes until 31 March 2027. It also says the sale of energy-saving materials by a retailer is always standard-rated. A kit bought online and fitted yourself carries 20% VAT. A system supplied and fitted by an installer in a home may qualify for the zero rate, depending on the facts; see our VAT guide.
Can I buy a unit and have you fit it?
We prefer to supply and fit, because we know the equipment, its condition and its history, and we can stand behind the commissioning. If you have already bought a split kit, ask us. We will look at the model and its condition, whether it suits the room and whether its pipe lengths and couplings work for your property, and give you an honest answer. If we fit it, it is commissioned and recorded properly, with F gas documentation.
If what you want is a quick, temporary fix for a heatwave, a portable unit or air conditioning hire may suit better than a DIY split. Our guide to fixed versus portable air conditioning compares the two.
Quick answers
Is it legal to install a pre-charged split system myself?
GOV.UK says qualifications are needed to install new air conditioning and heat pump systems, with no exemption for pre-charged equipment. Installation should be done by a qualified engineer working for an F gas certified company.
Why did a website sell me a kit without asking?
Sellers of non-hermetically sealed equipment are expected to ask for the installer’s details and check them. Their failure to ask doesn’t change the rules on installation.
Are portable air conditioners covered by the same rules?
Portable units are hermetically sealed appliances that plug in, so you can use them without an engineer. They have their own refrigerant rules.
Will you commission a system I’ve already fitted?
Talk to us first. We need to check the installation properly, and in some cases the safest answer is to redo the connections.
Related services
More advice
- Air Conditioning vs Portable Air Conditioner: Which Is Better?
- How to Find a Good Air Conditioning Engineer Near You
- Air Conditioning F-Gas Regulations: What Businesses Must Know
- 0% VAT on Air Conditioning and Heat Pumps: What HMRC Says
- 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.