Air conditioning is one of the few things you can buy for several thousand pounds where almost nobody knows what to ask. This is the list we would use ourselves — and it works just as well on us as on anybody else.
Why we have written this. A badly installed system is expensive, hard to put right, and often invisible until the warranty claim is refused. Most of what separates a good installation from a poor one is not visible when the job is finished.
Handling refrigerant legally requires personal certification, and a business doing it needs company registration too. Both are checkable. Ask for the numbers and look them up — REFCOM publish a register.
Public liability at minimum. If they are advising you on system sizing or design, professional indemnity as well. Ask for the certificate rather than the reassurance.
Air conditioning needs a dedicated circuit, and that is notifiable work under Part P. It should be done by a registered electrician who self-certifies it. The certificate should come to you in their name. If nobody can tell you who is doing the electrics, that is worth pausing on.
A fixed price is only meaningful if you know its assumptions. The most common variable is your consumer unit: if there is a spare way, the circuit is straightforward; if it is full or needs replacing, that is several hundred pounds. A good installer will have checked and told you at the survey.
A deposit covering equipment is normal. Being asked for the full amount up front is not. There is no reason the balance cannot wait until the system is installed, commissioned and working.
Scaffolding, making good, decorating, disposal of an old system, condensate pumps. None of these are unreasonable to charge for. All of them are unreasonable to discover on the day.
Most domestic installations are permitted development, but not all — and the rules changed in May 2025. Listed buildings and cooling-only systems are the usual exceptions. The full guide is here.
Since May 2026 this is the only accepted route for permitted development. It is a specific calculation with a specific output. Asking to see it is entirely reasonable, and the answer tells you a great deal. More on noise here.
Manufacturer warranties are almost always conditional on annual servicing, documented. A long warranty that lapses in year two because nobody serviced it is worth nothing. Ask what the term actually is, and what keeps it valid.
Registration is usually the installer's job and is easy to forget. A commissioning record — pressures, temperatures, electrical readings taken on the day — is the document that proves the system was set up properly. It also gives whoever services it next something to compare against.
The most revealing question on the list, because it is about the business rather than the equipment. How quickly would they come? Is there a call-out charge? Will they still be trading? The answer separates people who install air conditioning from people who look after it.
One honest note. We have written this list because we can answer all eleven, and we would rather compete on these than on price. But it is a genuinely useful list whoever you use, and you are welcome to take it to somebody else.
Written July 2026. If there is a question you think should be on this list, tell us and we will add it.
We would rather you asked and compared than took our word for it. Bring the list to your survey.
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