How to Choose an Air Conditioning Installer: What to Verify Before, During and After

How you choose an air conditioning installer comes down to three sets of documents: proof of certification and insurance before you sign, a room-by-room heat load calculation and an itemised written quote during the design and pricing stage, and a signed commissioning record after the units are on the wall. If a company can produce all three without hesitation, you are dealing with a competent installer. If any one of them turns into a vague reassurance, you have found a sales operation with a van.

The short version

• Before: F-Gas company certificate number (REFCOM, BESCA or Bureau Veritas), individual Category I certificates, £2m+ public liability and employer's liability insurance, confirmation of who handles Part P electrical notification.
• During: a site survey that opens the loft hatch and the consumer unit, a heat load calculation per room, and a quote that separates equipment, labour, electrical work, condensate/drainage, making good and removal.
• After: a commissioning sheet with pressures, temperature split, vacuum reading and added refrigerant charge, plus warranty registration and a system logbook.

How do you tell a competent installer from a good pitch before the refrigerant pipework is even run? You ask for the paperwork that a rushed installer cannot fake.

What does a trustworthy air conditioning installer look like?

Trustworthy is not a feeling. It is a short list of things you can check in an afternoon.

A trustworthy installer holds current F-Gas company certification, employs engineers with individual Category I refrigerant handling certificates, carries public and employer's liability insurance, and can hand you the certificate numbers rather than pointing at logos on a website footer. They size systems from a calculation, not from floor area. They write down what is and is not included. They commission the system against measured figures and give you the record.

Here is the position most guides shy away from: "get three quotes and read the reviews" is close to useless on its own. Three quotes for three different-sized systems, based on three different assumptions about your loft insulation and glazing, are not comparable numbers. A 300-review five-star profile tells you the company is pleasant to deal with, which is not the same as knowing whether the vacuum was pulled properly on your pipework. Reviews are a tiebreaker. Documents are the decision.

How to verify an air conditioning installer before hiring

Anyone who installs, services or decommissions equipment containing fluorinated refrigerant in the UK must be F-Gas certified, and the company employing them must hold company certification. This is legal requirement, not best practice. Start there.

Ask for, and actually check:

1. The company F-Gas certificate number. Certification is issued by bodies including REFCOM, BESCA and Bureau Veritas. Ask which scheme, ask for the number, then look the company up on that scheme's register. Trading names are easy to register and easy to change; the register tells you whether the name in front of you is actually the certified entity.
2. Individual engineer certificates. The person on your roof needs their own Category I qualification (City & Guilds 2079 or equivalent). Ask whose name will be on the job. If the answer is "one of the team", ask again.
3. Insurance schedules. Public liability of at least £2m, plus employer's liability if they have employees. Request the schedule, not a verbal figure. Goodman's contractor guidance puts licensing and insurance verification ahead of price comparison for exactly this reason [2].
4. Who notifies the electrical work. A dedicated circuit for an outdoor unit is notifiable under Part P in England and Wales. Either the installer is a registered competent person (NICEIC, NAPIT, ELECSA) or they use a subcontractor who is, or you need building control notification. Get the answer in writing.
5. Manufacturer accreditation. Daikin D1, Mitsubishi Electric's approved installer scheme, LG and Panasonic equivalents. These matter mainly because they unlock extended parts-and-labour warranties, often 5 to 7 years, that a non-accredited installer cannot register. Ask which warranty length your quote assumes.
6. Track record and references. Indoor Temp recommends at least ten years in the industry plus local references as a practical reliability benchmark [3]. In the UK market, where small AC firms come and go, a company that has been trading long enough to be honouring its own five-year warranties is a meaningfully different proposition to one incorporated last spring.

One more question worth asking early: does the property need planning permission for the external unit? Conservation areas, listed buildings and front elevations all complicate this. An installer who raises it before you do is thinking about the whole job.

What to check in an air conditioning installation quote

A quote is where competence becomes visible, because it is the written output of the survey.

The survey itself. A proper site visit takes 45 minutes to an hour, sometimes longer. The surveyor should look at glazing orientation and area, insulation levels, loft or void access for pipework, the position of the consumer unit and spare fuseways, condensate drainage options, and how each room is actually used. A home office with three monitors and a west-facing window is a different load to a north-facing bedroom of the same size. In period properties with solid walls and sash windows, glazing and fabric losses change the calculation further, which is one more reason a proper survey earns its place. If a company quotes from a phone call or a floor plan alone, that is not a survey.

The calculation. Ask for the heat load calculation, room by room, in kW. UK installers typically use manufacturer software or a CIBSE-based method rather than the American Manual J standard, so do not insist on Manual J by name; insist on the output. What you want to see is a stated cooling load per room and the selected unit capacity against it. Oversized units short-cycle, dehumidify poorly and leave rooms clammy. Undersized units run flat out and never quite get there. Sizing by "roughly 1kW per 10 square metres" is a starting rule of thumb, not a design.

The itemisation. A written quote should separate:

• indoor and outdoor units by model number, with stated capacities and SEER/SCOP figures
• pipework runs in metres, plus trunking or chasing and making good
• electrical work, including any consumer unit upgrade
• condensate pump or gravity drain
• scaffolding or access equipment
• removal of old equipment and waste, including refrigerant recovery
• commissioning and handover
• warranty terms, and what voids them

ENERGY STAR's contractor guidance goes further, and it is the point most quotes duck: a contractor should be able to show you the calculations behind expected savings from higher-efficiency equipment, rather than asserting them [1]. Heating and cooling is one of the largest single purchases a homeowner makes [1], and a poorly commissioned high-SEER system will underperform a well-commissioned mid-range one. If someone is charging a premium for efficiency, ask them to show the arithmetic. If you want a sense of where your numbers should land before you compare, our breakdown of what home air conditioning actually costs in the UK sets out typical ranges by system type.

How to check air conditioning installation after it's done

Ask for the commissioning sheet before the van leaves. This is the single most revealing document in the whole process, and the one most homeowners never request.

A proper commissioning record should show:

• Pressure test and vacuum: system pressure-tested with oxygen-free nitrogen, then evacuated. Look for a recorded vacuum figure (a decay test held after pulling down to around 500 microns, or 2 mbar). Moisture left in pipework is the single most common cause of premature compressor failure.
• Refrigerant charge: factory charge, pipe run length, and any additional charge added in grams. F-Gas rules require this to be recorded and the system labelled.
• Operating readings: suction and discharge pressures, superheat and subcooling, supply and return air temperatures. A healthy temperature split across the indoor coil is usually in the 8 to 11°C range in cooling.
• Electrical and controls: running current against nameplate, condensate drain test, controller and any Wi-Fi module paired and demonstrated.

You should also receive warranty registration confirmation, a system logbook, filter cleaning instructions, and the refrigerant type and quantity for your records. On smaller domestic splits using R32 (GWP 675), charges are typically well below the 5 tonnes CO2e threshold that triggers mandatory periodic leak checks, so annual statutory checks usually do not apply. Larger multi-split and commercial systems often cross it. Ask which side of that line your system sits on, because the answer determines your ongoing obligations.

Air conditioning installer requirements for homes, businesses and rentals

The same checklist, weighted differently. This is where generic advice fails people.

Homeowners: a bedroom split that is 3 dB(A) quieter matters more at 2am than any spec-sheet efficiency figure. Loft conversions and conservatories carry a heavier heat load than a ground-floor room of equal size; glazing area and roof insulation change the sums, which is why a proper room-by-room calculation beats a floor-area rule of thumb every time.

Businesses: a comms room needs an installer who will commit to a response window in writing and can explain what happens when a single unit fails, not just someone comfortable fitting a spare bedroom. Check the electrical supply early: a multi-head office system can draw enough load to push an existing board past its capacity, which is why office power requirements are worth checking before you commit to a layout. Commercial installs may also need building control involvement and, in leased premises, landlord consent.

Landlords: there is no AC-specific landlord certificate in the UK. What there is, in practice, is an expectation that you can produce evidence on request. Keep the installation and commissioning certificates, the electrical certificate, and the F-Gas documentation in the same folder as the EICR and gas safety record. Then write down, in the tenancy, who cleans the filters and who pays for annual servicing. Ambiguity there is where disputes start.

Air conditioning installer red flags to avoid

• No survey offered. A price quoted over the phone means the risk of getting the sizing wrong has been priced in, and you are paying for it.
• Verbal-only scope. "We'll sort the electrics" is not a line item. Get it in writing or expect a variation invoice.
• Piece-rate installation crews. Ask how installers are paid. Per-job pay rewards speed, and the corners cut first are the invisible ones: a shortened vacuum, an unbrazed joint left untested.
• High technician turnover. A quieter signal than any bad review, and a good reason to ask how long the lead engineer has been with the company. Indoor Temp's ten-year benchmark applies to firms; ask the same question of the people [3].
• Subcontractors with no named accountability. Fine in principle, but you need to know whose F-Gas certification and whose insurance covers the work, and who returns if there is a fault in year three.
• Aggressive discounting with a deadline. "This price is only good today" is a pressure tactic, not a pricing model.
• Efficiency claims without numbers. Adjectives instead of calculations, which is precisely what ENERGY STAR tells you to push back on [1].

How to choose an air conditioning installer: FAQ

What qualifications should a UK air conditioning installer have? Individual F-Gas Category I certification, employment by an F-Gas certified company, and either in-house Part P registration or a registered electrician for the circuit. Manufacturer accreditation is optional but unlocks longer warranties.

How do I know if an installer is F-Gas certified? Ask for the company certificate number and the issuing scheme, then check the register held by that scheme. Do not rely on a logo.

What is a heat load calculation and why does it matter? A room-by-room estimate of cooling demand in kW, accounting for glazing, insulation, orientation and occupancy. It determines whether your system is correctly sized, which affects comfort, running cost and equipment life more than the brand does.

Do landlords need special AC certification? No dedicated certificate, but you should hold installation, electrical and F-Gas documentation and record maintenance responsibilities in the tenancy agreement.

How long does installation take? A single split typically one day. A multi-split of three or four indoor units, two to three days. Commercial installs vary with access and electrical work.

How should I read installation reviews? Ignore the average. Read the three-star reviews and any negative ones for patterns in after-sales response, then ask for two references from jobs completed 18 months or more ago.

Next steps

This week, do three things. Email your shortlist asking for their F-Gas company certificate number, insurance schedule and a sample commissioning sheet from a recent job. Book surveys with the two who answer properly. Then compare the quotes line by line, checking that both are sized from the same room-by-room loads rather than the same rule of thumb.

If you would rather not start from a cold search of directories, you can request a quote and be matched with certified local installers who already work to that standard. Keep the commissioning sheet somewhere you will find it in seven years, when the warranty claim depends on it.

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