Will your electrics take air conditioning? Consumer units, spurs and what installers check

Most people booking a survey have thought about where the indoor unit goes and where the condenser sits. Almost nobody has thought about the fuse box. Then the surveyor asks to see the consumer unit, opens the cover, counts the spare ways and writes something down. That two-minute check decides whether your install is a clean one-day job or a two-visit job with an electrician in between.

What air conditioning actually draws

The kilowatt figure on a spec sheet is cooling output, not electricity used. A 2.5kW wall unit takes roughly 600 to 800 watts from the wall when it is working hard, which is under 4 amps. A 3.5kW unit sits nearer 1kW, and a 7kW multi-split condenser serving three heads might peak around 2.2kW.

Those are small numbers. A kettle pulls more. The reason air conditioning still needs proper attention is not the size of the load, it is that the load runs for hours at a time, sits outdoors, and has to be isolated safely for anyone working on it.

Inverter units start softly rather than slamming on at full current, so the old worry about a compressor tripping the lights is largely gone on modern equipment.

Why it needs its own circuit

Fitted air conditioning is fixed wiring, not an appliance you plug in. The condenser is fed from a dedicated circuit at the consumer unit, through a switched fused connection unit or an MCB, and terminated at an isolator by the outdoor unit.

There are three reasons for that. The circuit can be switched off on its own without killing the sockets in half the house. It cannot be unplugged by accident or shared with a load that pushes it over. And anyone working on the outdoor unit can lock it off and prove it dead before touching refrigerant pipework or fan blades.

In England and Wales, adding a new circuit is notifiable work under Part P of the building regulations. It must be done by a registered electrician who self-certifies it, or notified to building control. Ask which applies before the day. Scotland works to its own building standards, with the same practical outcome.

What the surveyor is checking

Four things, and they take longer to write down than to look at.

Spare ways. A modern board has room for another MCB or RCBO. A board that is full needs either a small sub-board next to it or a replacement.

Protection type. Boards fitted since 2016 usually have RCBOs on each circuit. Older split-load boards from the 2000s have two RCDs covering banks of circuits. Either can be worked with. A rewireable fuse box with ceramic carriers and no RCD at all cannot take a new circuit as it stands.

Main fuse rating. Most UK homes have an 80A or 100A supply head, and a few older properties still have 60A. Air conditioning on its own is never the problem. It becomes a problem when it joins an electric shower, an induction hob and an EV charger on a 60A supply.

Cable route. The distance from the board to the condenser position decides cable size and how much of the job is chasing, clipping or running in trunking.

When the electrics need work first

If the board has a spare way and RCD protection, the new circuit is a small addition on install day. Budget £120 to £250 on top of the quote, and expect it to be done by the installer’s electrician while the refrigeration work carries on.

If the board is full, unprotected or a rewireable relic, you are looking at a consumer unit replacement before the air conditioning can be fitted. That is a separate visit and typically £450 to £900 depending on the number of circuits and whether the existing wiring passes its checks. It is not wasted money, since the board serves the whole house, but it needs to appear on the quote rather than on install day as a surprise.

Older properties are where this comes up most. Our guide to air conditioning in old houses and cottages covers the other things that catch out pre-war buildings.

The outdoor isolator

Every fitted system gets a rotary isolator on the wall near the condenser, usually a small grey box with a red and yellow switch. It is there so an engineer can kill the supply at arm’s length rather than trusting somebody indoors not to switch it back on.

Do not use it as an off switch during normal running. Cutting power at the isolator stops the crankcase heater on some units, and on others it wipes the settings. Use the remote or the wall controller and leave the isolator alone.

EV chargers, heat pumps and the supply limit

This is the 2026 version of the question. Plenty of North West homes now have a 7kW EV charger, and a growing number have an air source heat pump. Add air conditioning and you are stacking three continuous loads onto one supply.

Your electrician works out the total demand with diversity applied, which allows for the fact that these things rarely all peak together. Where the sums are tight, the usual answer is a load-limiting device that throttles the EV charger when the rest of the house is drawing heavily, rather than an expensive supply upgrade. A supply upgrade from the network operator is the last resort and can take weeks, so it matters that this gets spotted at survey and not later.

If you have solar, the picture changes for the better on running costs. Our post on running air conditioning from solar panels goes through the numbers.

Three things to ask before you sign

Is the dedicated circuit included in the price, or listed separately? Who does it, and are they registered for Part P self-certification? Will I get an electrical installation certificate or minor works certificate on completion?

A quote that covers all three is a quote from somebody who has done this before. Our 12 questions to ask an installer has the rest of the list.

Get the electrics priced in from the start

Mention your consumer unit on the quote form: roughly how old it is, whether it has a row of small switches or old fuse carriers, and whether you have an EV charger or a heat pump. Installers can then price the circuit properly rather than guessing. Three fixed quotes back within 24 hours from vetted North West installers.

Or check the prices page for a rough bracket first, or email us a question if you want to talk it through before requesting quotes.