Ask an air conditioning installer how the cooling load was calculated, how ventilation and heat reduction were considered, who will perform refrigerant work, what permissions are needed, and exactly what the quotation includes. Also ask about noise, drainage, electrical work, controls, commissioning, warranty, maintenance, records and response if performance falls short. Good answers should be specific to the property and documented.
Start with how they sized it
A credible proposal explains the inputs, not just the kilowatts. Ask what they assumed for a hot afternoon, how many people use the room, what the glass does, whether a roof sits over it, and how many hours it will run. If the capacity came only from the floor area, ask what that leaves out. Loft rooms, bifold doors and a shop with the door open are the usual misses.
Ask whether shading, ventilation or simply not cooling the whole house would change the machine. A split recirculates the air in the room. It is not a ventilation system and it does not bring in outdoor air. If the room is stuffy because it has no extract, cooling alone will not fix that.
Then ask why this type of indoor unit. A wall box, a floor console, a ducted run or a cassette are different holes in the building. The right question is which one fits the room you have, including where the air will blow. A unit aimed at a bed or a treatment couch is a design failure even if the maths was tidy.
- What conditions did you design for, indoors and outdoors?
- How did solar gain and the hours of use get into the figure?
- Why this indoor type for this room?
- What happens if the room is only partly loaded on a mild day?
Who is allowed to do which part
For equipment that contains regulated F-gas, ask for the company certificate and the qualification of the person who will braze, pressure-test, evacuate and charge. GOV.UK sets out both the company certification and the qualifications. An engineer's card on its own is not always the whole requirement. Company certification can be required as well.
Then separate the other trades. Who runs the new circuit, who drills the wall, who fire-stops a hole through a compartment, and who is insured for work at height? A firm can subcontract those. You still want the names, and you still want the refrigerant work tied to a certified company.
Insurance and a method statement should describe your job. A generic PDF that never mentions a ladder, a flat roof or a listed wall is paperwork, not a plan. Ask who is checking planning, the lease and any landlord approval. You remain responsible for permissions. The installer can supply the drawing and the noise data. They cannot decide the application for the council.
The outdoor unit, the drain and the neighbour
Ask where the outdoor unit will stand or hang, in a sentence you could point at on a photo. Then ask about noise at the nearest bedroom window, yours and next door's, how it is isolated from the wall, and how a person will service it in three years without another scaffold. A position that only works if nobody sleeps nearby is not a position.
Ask where the water goes. Gravity to an outside spout, a pump to a waste, or a hope that it drips on the path are three different answers. Ask what you will notice if a pump fails. Indoor water on a landing is the usual teacher.
If you are in a flat, ask what they need from the freeholder before they order equipment. If the building is listed or on a street in a conservation area, ask them to say so in the quote. In England, Class G is not a permission for a unit used only for cooling, and it does not apply to a listed building. A quote that says "no planning needed" without the property type and the outdoor spot is a guess.
Take the quotation apart
The quotation should identify models, quantities, controls, included pipe length, the rate for extra pipe, electrical supplies, isolators, the condensate arrangement, access equipment, builders' work, finishes and waste. If any of those say "by client" or "extra", treat them as part of the price you still have to pay.
Ask what is excluded, who fills and paints, whether every filter and drain can be reached after the furniture goes back, and what the household should expect on the day: power off, floors covered, how long, who must be in. Avoid comparing two totals when one of them left the electrics out.
For a shop or an office, ask about working hours, whether the system is large enough that inspection duties over 12 kW could apply, and who keeps the log. A domestic-style quote pasted onto a commercial job usually forgets access out of hours and the drain above a sales floor.
- What is outside the fixed price?
- Who makes good the walls and the decoration?
- Can the filters, the drain and the isolator be reached later?
- What has to stop in the building while they work?
Handover, warranty and the hot week you have not had yet
Ask what commissioning will measure and what you will hold in your hand afterwards: model and serial numbers, the pressure test and vacuum record, the refrigerant type, the control instructions, the warranty registration, and a sketch of where the pipes and the drain went. Agree how a problem that only shows up in the next heatwave will be judged. A handover in April does not prove July.
Read the warranty as two promises. One is the manufacturer's parts. The other is who will attend, in what hours, and what they charge to look. Ask what maintenance keeps the warranty valid. Ask what is excluded: filters, pumps, labour, travel. A long warranty with no labour and no local attendance is a thinner promise than the brochure.
If performance is poor, you want a written route: who you call, how fast, and what counts as a defect rather than a room that was never going to cool with the door open. Keep the quote, the certificates and the photos of the finished pipe run. Those are what you will need if the firm changes its name before the first service.
Frequently asked questions
Should I choose the installer offering the largest system?
No. Larger is not automatically better. Oversizing can impair control and efficiency. Choose a justified design based on calculated loads, suitable zoning and credible operating assumptions.
How can I verify F-gas credentials?
Ask for the company certificate and technician qualification details, then verify them with the issuing certification body where possible. GOV.UK explains which qualifications and certifications are required.
Should a quote include planning permission?
Do not assume it does. The quotation should state who checks and obtains planning, landlord or other approvals. The applicant remains responsible for ensuring the necessary permissions are in place.
What should happen at handover?
The installer should commission the system, demonstrate controls and provide agreed records, warranties and maintenance information. Record any incomplete work and the date for resolution.
Is a long warranty enough evidence of quality?
No. Check what it covers, labour and travel terms, maintenance conditions, response arrangements and who supports it if the installing business changes.
Core buying guides
Start with these high-intent guides, then dig into the rest of the library.
Related guides
Sources and further reading
How this guide was prepared
This guide was written by the Local AC Installers Editorial Team. We compare official guidance, legislation and established consumer information, separate general information from project-specific advice, and show publication dates and sources. We do not accept installer accreditation claims at face value.