Less time than most people expect. A single-room split system is usually fitted in a day — the engineers arrive in the morning and, for a straightforward job, you're cooling the room that evening. A multi-split serving three or four rooms typically takes two to three days. It's disruptive in the way a washing machine delivery is disruptive, not in the way a new kitchen is.
Typical timescales
| Job | Typical time on site |
|---|---|
| Single-room split | Usually one day |
| Multi-split (two rooms) | One to two days |
| Multi-split (three to four rooms) | Two to three days |
| Ducted / whole-home | Roughly a week, sometimes more |
These assume the survey has been done and any groundwork (electrics, scaffolding, permissions) is sorted before the install date. That last part matters more than the headline numbers, as we'll get to.
Before the day: the survey
A proper installer won't just turn up with a van full of kit. They'll survey first — usually a short visit — to agree where the indoor unit sits, where the outdoor condenser goes, the route the pipework takes between them, and whether your fuse board can take the extra circuit. If your electrics need attention first (an ageing consumer unit, no spare way, no recent safety certificate), that work happens before install day, not during it. Our guide on whether your home electrics can handle air conditioning covers how to tell where you stand.
What actually happens on install day
The sequence is fairly standard, and knowing it helps the day feel less mysterious:
- Setting up. Dust sheets down, positions confirmed with you one last time. Speak up now if you've changed your mind about where anything goes — it's a five-minute conversation at 8am and a headache at 3pm.
- Mounting the indoor unit. A bracket goes on the wall, high up, usually on an external wall to keep the pipe run short.
- The core drill. A single neat hole through the wall for the pipes, cable and condensate drain. This is the noisiest, dustiest part of the day, and it doesn't last long.
- Pipework and cabling. Copper refrigerant pipes, a power cable and a small drain pipe run from the indoor unit to the outdoor one, normally hidden in white trunking on the outside wall.
- The outdoor unit. The condenser is fixed to a wall bracket or ground-level base, then connected up.
- Vacuum, test and commission. The engineer vacuums the pipework with a pump to pull out air and moisture, pressure-tests it, releases the refrigerant and runs the system in both cooling and heating modes. This stage is why installation isn't a DIY job — anyone handling refrigerant must hold F-Gas certification, and it's not something to attempt yourself under any circumstances.
You should finish the day with a working system, a demonstration of the controls, and the paperwork — commissioning record, warranty details and F-Gas documentation. Keep them; you'll want them if you ever need a repair or service down the line.
How much mess is there?
Honestly, not much. The core drill produces dust, but any decent installer sheets up and many use extraction on the drill. There's a bit of drilling for brackets and some offcuts of trunking to sweep up. Making good is minimal — the hole through the wall is sealed and covered, and the trunking outside is the main visible change. If tidy trunking routes matter to you (they often do on period frontages), agree the route at survey stage, not on the day.
Do you need to be home?
For the first hour, yes — final decisions on positions are yours to make. And for the last half hour, ideally — the handover and controls demo are genuinely useful. In between, most installers are happy for you to work from home, do the school run or go out entirely, as long as they have access to the rooms they need and somewhere to make tea. Ask when you book; every firm has its own preference.
What turns one day into two or three
- Scaffolding or access kit. If the outdoor unit is going on an upper wall or a flat's balcony, working at height needs proper access, which needs arranging in advance. This is one of the most common causes of a delayed start.
- Awkward pipe runs. If the indoor unit sits far from any external wall, pipes may need routing through a loft or void. Longer runs mean more hours (and typically more cost — our cost guide explains what drives the price).
- Electrical work first. If a consumer unit upgrade or safety inspection is needed, that's a separate visit before the AC install. Better to know at survey than on the morning.
- Permissions. Flats often need freeholder or management-company consent for an outdoor unit, and listed buildings need consent for external changes. Paperwork moves slower than engineers do.
None of these are reasons to worry — they're reasons to have a thorough survey, so the install day itself runs smoothly.
Booking it in
Lead times stretch in a heatwave, when everyone wants cooling at once, and shorten noticeably in spring and autumn. If you're planning ahead, the quiet months are a good time to get quotes. When you're ready, tell us about your home and we'll match you with one vetted local installer — not a bidding scrum — for a free survey and a no-obligation quote.