A practical guide to planning a fixed air conditioning installation in the UK: which system type to choose, how kW sizing works, what happens on site and what shapes the final price.
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A fixed air conditioning system is a long-term piece of building services equipment. Treat it like a gadget and you'll regret it. Fitted well, a modern split system cools a room quietly in summer, heats it efficiently in winter and keeps going for years with nothing more than routine servicing. Fitted badly, the same kit can be noisy, leak refrigerant, drip water down a wall and cost more to run than it should.
This guide follows an installation from the first decision through to the first service visit. It's written for UK homes and businesses, so we talk in kilowatts (never "tonnes") and about split and multi-split systems, with no window units in sight. It also covers the rules that apply here, such as F-Gas certification and local planning rules for outdoor units.
An air conditioning installation means fixing an indoor unit inside the room, an outdoor unit (the condenser) outside the building, and connecting the two with insulated copper refrigerant pipes, a communication and power cable and a condensate drain. The pipework is then pressure tested, evacuated and charged, and the system is commissioned and handed over with its paperwork.
Nearly every UK installation follows that pattern. The differences between jobs are in the type of indoor unit and the distance between the two halves. How the pipework gets hidden varies too, along with how many rooms one outdoor unit serves.
Read an American guide and you'll see "central air", window units and portables presented as the standard choices. Things are different here. Ducted whole-house systems are unusual, because most British homes are heated by radiators and have no ductwork to start with. Window units rarely work with sash, casement or uPVC windows. You can buy a portable, but it vents hot air through a hose, it's fairly loud and it's far less efficient than a fixed system. For a permanent installation you're realistically choosing between four types.
One indoor unit, usually high on a wall, connected to one outdoor unit. You'll find more of these in homes and small offices than anything else. They're quick to fit and easy to service, and they need just one core hole of around 65mm through the wall. Our guide to wall-mounted air conditioning units covers placement in more detail.
Two or more indoor units, each controlled separately, running from a single outdoor unit. If several bedrooms or offices need cooling but there's only room for one condenser outside, a multi-split is normally the answer. The pipe runs are longer, so the routes through lofts, floor voids and cupboards need planning carefully. See our multi-split installation guide for how the routes are designed.
A concealed indoor unit sits in a ceiling void, loft or bulkhead and delivers air through short ducts to grilles in one or more rooms. Only the grilles and a controller are visible. They make most sense in new builds, extensions, loft conversions and refurbishments where the ceilings are already open. Retrofitting ductwork into a finished room means a lot of building work.
A cassette unit fits flush into a suspended or plasterboard ceiling and blows air in up to four directions. Cassettes are the standard choice for offices, shops and restaurants, and we're seeing more of them in large open-plan kitchens and living spaces. You need a deep enough ceiling void and a route for the condensate, which a built-in pump often takes care of. As the unit sits in the ceiling grid, it's best planned at the same time as any other ceiling or lighting work.
UK air conditioners are rated in kilowatts (kW) of cooling capacity. Rules of thumb from abroad, such as "one ton per 500 square feet", don't work well for British buildings, where insulation, window areas and summer temperatures tend to be different. Typical domestic split sizes here are 2.0, 2.5, 3.5, 5.0 and 7.0kW.
Floor area alone won't tell you the right size. You have to look at the whole room, and an installer should consider:
Go too small and the unit runs constantly without ever quite reaching the set temperature. Go too big and it cycles on and off, wasting energy and doing a poorer job with humidity. Our post on what size air conditioning unit you need goes into the calculation.
Most installation problems can be headed off at the survey. A good one settles four things before anyone drills a hole.
The indoor unit needs clear space around it for airflow and a sensible route for pipework and drainage. It also needs to be somewhere the air spreads across the room instead of blasting straight at a bed or desk. Above a door, or on the wall facing the main seating area, are the usual spots.
The condenser needs free airflow and a solid wall or level base. Think about the neighbours, and make sure an engineer can get to it safely for servicing later on. Wall brackets and ground stands are both common, fitted with anti-vibration mounts. Avoid corners that trap heat or bounce sound around.
Plenty of outdoor units go in without a planning application, but it depends on the property and where it is. Listed buildings, conservation areas and units on prominent elevations need extra care, and in a flat you'll usually need written consent from the freeholder or managing agent. UK Aircon checks with the local planning authority where it applies.
A smaller domestic split can often go on a suitable existing circuit. Larger systems may need their own supply from the consumer unit. We confirm this at the survey, so nothing comes as a surprise on the day.
A single wall-mounted split is usually done in a day. Multi-split, ducted and commercial systems take longer, and we agree the timescale when we quote. The work itself splits into four phases.
The indoor unit's backplate is fixed level, the core hole is drilled with a slight fall to the outside, and the outdoor unit is mounted on its brackets or stand.
Insulated refrigerant pipes, the interconnecting cable and the condensate drain are run between the units, with trunking or boxing where pipes would otherwise be visible.
The pipework is pressure tested with nitrogen to confirm it is leak-tight, then evacuated with a vacuum pump to remove air and moisture.
Refrigerant is released into the system, it is run in cooling and heating, readings are recorded and the controls are explained to you.
Inexperienced installers rush the proving stage more than any other, and it's the stage that matters most. Skip a proper pressure test or vacuum and you can leave moisture or a small leak in the system. Months later that turns up as poor performance or a dead compressor, the sort of fault our air conditioning repair guide deals with.
Anyone handling refrigerant must hold an F-Gas qualification, and the business they work for must hold F-Gas company certification. REFCOM is one of the certification bodies, and UK Aircon is REFCOM registered. It's a legal requirement and not a quality badge. The rule exists because refrigerants are greenhouse gases, and leaks do real environmental harm.
Check for certification before you accept any quote. Our engineers hold it on every job, from Newcastle to sites where we provide air conditioning in Manchester. Most manufacturers also want proof that a qualified installer fitted the equipment before they'll honour their own warranty.
UK Aircon installations start from £1,800 installed. How far above that a particular project comes in depends on the factors below, and that's why we quote after a free survey instead of working from a price list.
| Factor | Why it affects the price |
|---|---|
| Number of indoor units | Each additional room adds equipment, pipework and labour. |
| System type | Ducted and cassette units involve ceiling work that a wall-mounted split does not. |
| Capacity | Larger kW units cost more and may need a dedicated electrical supply. |
| Pipe run length and route | Long runs through lofts, floors or multiple storeys take more time and materials. |
| Outdoor unit position | High-level brackets or awkward access may need extra equipment. |
| Condensate drainage | If water cannot drain by gravity, a condensate pump is required. |
| Making good and finishing | Trunking, boxing-in and decoration around pipe routes add to the job. |
Running costs are a different matter. They come down to how you use the system and what tariff you're on. Our article on what air conditioning costs to run shows how to work them out.
At handover you should receive the commissioning details, the warranty information and a clear explanation of the controls, including how to clean the filters. Hang on to these documents. You'll want them for servicing, for any warranty claim and if you ever sell the property.
UK Aircon installations come with a 5-year warranty covering parts and labour, which also includes access to 24-hour emergency call-out, complimentary maintenance check-ups and discounted spares. We recommend a service once a year to keep the system efficient, and more often for commercial or heavy use. Our guide to air conditioning maintenance explains what a service involves.
A single wall-mounted split system is usually installed in one day. Multi-split systems serving several rooms, ducted units and commercial installations take longer, and the expected duration is confirmed in the quotation after the survey.
Yes. Installation can be carried out at any time of year, and because modern split systems are air-to-air heat pumps, a unit installed in winter can be used for heating straight away. Installers are often less busy outside the summer months.
Many outdoor units do not need a planning application, but it depends on the property and location. Listed buildings, conservation areas and prominent elevations need extra care, and flats normally need the freeholder's consent. A good installer checks with the local planning authority where it applies.
Connecting and charging a split system involves handling refrigerant, which legally requires an F-Gas qualified engineer working for a certified company. DIY installation also usually invalidates the manufacturer's warranty and risks leaks and poor performance.
A typical wall-mounted split needs a single core hole of around 65mm for the refrigerant pipes, cable and condensate drain. It is drilled with a slight fall to the outside so water runs away from the building.
A portable unit can provide temporary relief but vents hot air through a hose, is louder and is far less efficient than a fixed split system. For regular use over several summers, a fixed installation is usually the better long-term choice.
Thinking about a new system for your home or workplace? UK Aircon's REFCOM-registered engineers can survey the space, recommend the right type and size, and give you a clear written quote. Start with our domestic air conditioning installation or commercial installation pages, or request a free quote and we will reply within 24 hours.
The wall-mounted split is the most common air conditioner in UK homes and small offices. Where it goes, how it is fitted and how it is set up decide how well it performs for the next decade.
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Read article : Commercial Air Conditioning: Optimal Systems, Maintenance Tips, and Energy SavingsFree, no-obligation quotes from REFCOM registered installers with over 20 years of experience. Locally owned and operated, with a 5 years warranty.
