In a UK heatwave, the 2.5 kW and 3.5 kW wall splits everyone wants, and the F-gas installers who fit them, get booked out together. As a 2026 illustration, do not expect a surveyed install in the week a hot spell is forecast if you have not already been quoted. Lead times move from a fortnight in a quiet spring to many weeks once the diaries fill. Rushing is how outdoor units end up under bedroom windows. Buy after a survey, not from a marketplace listing at midnight.
The pairs everyone wants, and the vans that fit them
Distributors hold a finite number of popular Daikin, Mitsubishi and similar pairs. When London, the South East and then everywhere else hits the same temperature, those pairs are allocated to firms who already had orders. A website that still shows a photo is not the same as a unit in a local warehouse.
Installers cannot invent extra vans. A company that answers the phone may be offering August or September. Anyone offering tomorrow, without a survey, is the quote to read twice. Popular bedroom sizes go first. A proper survey still has to happen.
The nearest wall, the size that is in stock, and a spring survey
The outdoor unit goes on the nearest wall. The drain goes into a flowerpot. The electrical supply is an extension lead story that should never have been offered. Noise, staining and a refused freeholder are the autumn consequences of a July rush.
Different kW is the other rush error. The size that is in stock is not the size the room needs.
Ask for surveys in spring, or at least before the first run of hot nights. You can then choose the outdoor position, ask the freeholder, and let an insurer or a planner answer while the house is still comfortable. Equipment can be ordered against that survey. Planning, lease and party wall questions do not pause for the weather.
As a 2026 illustration, a quiet-season install on a straightforward house still sits in the high hundreds to a few thousand pounds including VAT. Heatwave premiums show up as waiting, out-of-hours rates, or a thinner choice of model, not as a better system. Diaries ease and choice returns later. Do not count on a dramatic equipment crash. Energy Saving Trust describes air-to-air heat pumps. GOV.UK F-gas commissioning cannot be skipped to save a day. Daikin and Mitsubishi Electric pairs are the ones that disappear first, not a reason to buy a lone indoor online.
A portable for a few nights, not a bad bracket forever
If you are already in the hot week, still insist on a visit, a kW and a lawful outdoor spot. A portable can bridge a few nights. It is a poor reason to accept a permanent condenser in the wrong place. Confirm the company is F-gas certified before they attend.
Say which rooms must be first if stock is limited. A written place in a diary beats refreshing a basket.
Frequently asked questions
Can I get air conditioning installed the same week as a heatwave?
Sometimes, if a local firm has a gap and the right unit, and the job is simple and already allowed. Often you cannot. Assume you need a survey and a wait, and treat same-week promises with caution.
Should I buy an indoor unit online while I wait?
No. Splits are matched pairs commissioned by an F-gas company. A lone indoor from a marketplace is not a head start. Let the installer supply the pair they will warrant.
Will prices drop again in September?
Diaries ease and choice returns. Do not count on a dramatic equipment crash. The saving is a better siting decision and a unit that matches the room, which is worth more than a seasonal sticker.
Is the size in stock the size the room needs?
Not by itself. A 2.5 kW unit fitted because the 3.5 kW is on backorder will not grow in the next heatwave. The survey still names the duty.
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.