The short answer
Ask how they sized the system, where both units and the pipes will go, whether it meets planning and noise rules, what the quote includes, which F-gas and electrical qualifications they hold, and what warranty and servicing come with it.
On this page
Quotes for the same room can look alike on paper and still differ a lot in what they include and how carefully the job has been planned. Asking every installer the same questions makes quotes easier to compare, and a good installer will be happy to answer them clearly and in writing.
The system and its size
The answers here tell you whether the system has been chosen for your room or just picked from a price list.
- How did you work out the size, and what did you measure?
- Will it heat as well as cool, and how much heat does it give in cold weather?
- What are the noise figures for the indoor unit on its lowest fan speed, and for the outdoor unit?
- What are its SEER and SCOP figures?
- Which refrigerant does it use?
- If more than one room is involved, why this arrangement rather than separate systems or a multi-split?
A good answer on sizing mentions the room's windows, which way it faces, the insulation and how you use it, not only the floor area. The sizing guide explains what should go into it.
Where everything will go
Ask to see the positions marked out, or drawn on a plan, before you agree to anything.
- Where exactly will the indoor unit, the outdoor unit and the pipes go?
- How long is the pipe run, and will it need extra refrigerant?
- What will the pipework look like, inside and out, and will it be covered?
- Where will the condensate drain go, and will it need a pump?
- Will the outdoor unit go on a wall bracket or a ground stand, and what stops vibration?
- What holes will be drilled, and how will they be sealed and made good?
Planning, noise and electrical work
Rules differ across the UK. The planning and noise points below apply to England, and Scotland, Wales and Northern Ireland have their own rules.
- Does the installation meet the permitted development conditions, or will it need planning permission?
- Have you done the MCS 020(a) noise calculation for the outdoor unit, and can you give me a copy?
- My home is listed, or in a conservation area: what does that change?
- Does it need a new electrical circuit, who will do that work, and how will it be notified?
The noise calculation checks the outdoor unit against a limit of 37 dB(A) at 1 metre from the nearest window or door of a habitable room in a neighbouring home. The installer keeps the calculation, and you should get a copy. The planning permission guide covers the conditions in more detail.
Listed buildings need listed building consent, and permitted development doesn't cover them. Conservation areas have stricter rules, including on walls and roofs facing a road. If you live in a flat, or your home's permitted development rights have been removed, different rules apply, so check with the local council. Leaseholders should check the lease as well.
In England and Wales, a new circuit is notifiable under Part P of the Building Regulations. It should be done by an electrician registered with a competent person scheme, or notified to building control.
Qualifications and insurance
Split systems are connected into a sealed refrigerant circuit on site, so the work needs qualified people.
- Do the engineers doing the refrigerant work hold the right F-gas qualification?
- Does the business hold a company F-gas certificate?
- Who does the electrical work, and are they registered?
- What insurance do you have in case something is damaged during the work?
Why installation needs a certified engineer explains what these qualifications cover.
The quote, warranty and aftercare
A detailed written quote protects you both, and makes it clear what would count as extra.
- Is everything included: equipment, brackets, pipe covers, electrical work, drainage, making good and removing packaging?
- What would cost extra, and in what circumstances?
- What warranty covers the equipment, and what covers the workmanship?
- Does the warranty depend on regular servicing, and who can carry it out?
- How often should the system be serviced, and do you offer servicing?
- Who do I contact if something goes wrong, and how quickly do you usually respond?
At the end of the job you should receive paperwork that matches what you were told.
| Document | What it's for |
|---|---|
| Written quote | What was agreed and what it included |
| Noise calculation | Shows the outdoor unit meets the limit |
| Electrical certificate | Confirms the circuit was done and notified |
| Commissioning record | The tests done and any refrigerant added |
| Warranty details | What's covered, for how long, and on what terms |
| Manuals | How to use and look after the system |
Related guides
- What size air conditioner do you need?Most bedrooms and smaller living rooms suit a unit of about 2.0 to 3.5 kW, and large open-plan spaces often need 5.0 kW or more. Sun, glazing, insulation and ceiling height can matter as much as floor area.
- Do you need planning permission?Usually not in England, where air-to-air heat pumps that aren't used only for cooling count as permitted development if conditions on number, size, position and noise are met. Listed buildings, flats and protected areas follow different rules.
- Why installation needs a certified engineerA split system is joined into a sealed refrigerant circuit on site, and in Great Britain anyone doing that work needs the right F-gas qualification, with the business holding a company F-gas certificate. Poor work can cause leaks, damage and safety problems.
- Commissioning and handoverCommissioning is the set of tests that prove a new system is sealed, safe and working as designed. Handover is when the engineer shows you how to use and look after it and gives you the records and certificates to keep.