Air conditioning for home offices and garden rooms

For a permanent working-from-home setup, the best home office air conditioning is a wall-mounted reverse-cycle split. It cools the room properly in a heatwave, and because it is an air-to-air heat pump it also heats the same room in winter, which is exactly what you want for a space you sit in all year. The same unit is the right answer for a detached garden room or garden office. Expect to pay roughly £1,500 to £3,000 supplied and fitted, and for a garden room, budget separately for a proper electrical supply.

A portable unit will get you through a single hot week, but it is a stopgap, not a fix, and it is too noisy to have running behind you on a video call. This guide covers both spaces side by side: the home office inside the house (usually a spare bedroom) and the detached garden room, which overheats in summer and freezes in winter. It walks through which system to choose, how to keep it quiet enough for calls, what it costs to run during the working day, how to get power to a garden room safely, and the planning rules that catch people out.

Home office or garden room: which system

The space you are cooling changes the practical detail more than the choice of unit. For both, a wall-mounted reverse-cycle split is the sensible default. The differences are the power supply and the planning.

The real decision for most people is a fixed split versus a portable, and being honest about that saves a disappointing summer of trying to work in a hot room. A fixed split holds the whole room at a temperature you set and runs quietly in the background. A portable helps a little in one spot, roars while it does it, and vents warm air back through the window or door it needs for its hose.

Why garden rooms overheat, then freeze

A garden room is one of the hardest spaces in the country to keep comfortable, and it is worth understanding why before you spend money.

It combines three problems. There is a lot of glazing, so sunlight pours in as solar gain and heats the room fast. The structure is usually lightweight timber with low thermal mass, meaning there is little heavy material to soak up and slow that heat, unlike a brick house. And it sits out in full sun with no shading from the main building. Put together, a garden room can become uncomfortable by mid-morning on a warm day and unusable by the afternoon.

The same features work against you in winter. A thin, glazed, timber structure loses heat far faster than an insulated cavity wall, so the room that was too hot in July is often too cold to work in from October. That double problem, too hot then too cold, is exactly why a unit that both cools and heats makes so much sense here. A reverse-cycle split is an air-to-air heat pump: flip it from cooling to heating and it warms the room efficiently through the colder months, so the garden office earns its keep all year rather than sitting empty half of it.

The options explained

Wall-mounted single split. Best for: almost every home office and garden room. One indoor unit, one outdoor condenser, quiet and efficient, and it cools and heats. For these spaces a 2.5kW or 3.5kW unit is usually the right size. This is the unit to picture when you read the rest of this guide, and you can see the range on our wall-mounted split systems pages.

Multi-split. Best for: cooling the home office and another room from one outdoor unit. If you want the spare-bedroom office cool by day and a bedroom or living room cool in the evening, a multi-split runs several indoor units off a single outdoor condenser, which keeps the outside of the house tidier. It costs more, scaling with the number of indoor units.

Self-contained unit with no outdoor unit. Best for: a garden room where there is nowhere sensible to put an outdoor condenser, or where you do not want one on show. These vent through two small holes cored in the wall and plug into a normal socket, with some models running at around 27 dB(A). They are a niche answer but a genuinely useful one. We cover them fully in our guide to air conditioning without an outdoor unit.

Portable. Best for: a renter, or a single hot week while you decide. A portable unit is the honest quick fix: a few hundred pounds, no installation, cooling today. The catch is noise (more on that next), lower efficiency, and the open window or door the hose needs, which lets warm air and cooling straight back out. As a long-term working-from-home solution it disappoints. If a portable is your only option, our guide to the quietest portable air conditioners will help you pick the least intrusive one.

For a fuller walk-through of the choice, see how to choose an air conditioning system.

Keeping it quiet enough for video calls

This is the concern that separates a working-from-home buyer from everyone else, and it is the strongest reason to choose a split over a portable.

Noise is measured in dB(A). A whisper is about 20 dB(A) and a quiet library about 40 dB(A). The quietest wall-mounted splits run at roughly 19 to 21 dB(A) indoors on their lowest setting, which is genuinely whisper-quiet and vanishes into the background of a call. A portable, by contrast, runs at around 42 to 65 dB(A), often near 55 dB(A), because its compressor, the noisy part, sits inside the room with you rather than outside. That is close to the 60 dB(A) of normal conversation. On a call it is the difference between silence and a steady roar behind your voice.

A split puts the noisy compressor outside; a portable keeps it in the room with you, which is why it shows up on every call.

If calls matter, choose a split with a quiet or night mode and you will forget it is running. If you are stuck with a portable, run it on a low fan speed, position it away from the microphone, and expect to mute between speaking.

What it costs to run during work hours

Running costs during the working day are modest, which surprises people who assume air conditioning is expensive.

Take a 2.5kW unit, the typical size for a home office or a small garden room. When it is actively working it draws around 0.6kW. At the current electricity price cap of 26.11p/kWh, that is 0.6 x 26.11p, or about 16p an hour. Over an eight-hour working day it uses roughly 4.8kWh, which is 4.8 x 26.11p, or about £1.25 a day, and about £6.27 across a five-day week. A larger unit working hard in a very glazed room on the hottest days can climb toward 26p an hour, but you will rarely run flat out all day, because an inverter split eases back once the room reaches the temperature you set. From 1 October 2026, VAT on domestic electricity is cut from 5% to 0%, which will trim these figures slightly.

Two things keep the cost down. A fixed split is far more efficient than a portable, and once it has cooled the room it only sips power to hold that temperature. Choosing a unit with a high efficiency rating (look for A++ or A+++, and a high SEER for cooling and SCOP for heating) pays for itself over the years you will use it.

Prices and rates correct as of July 2026. The energy price cap changes quarterly, so check current rates before budgeting.

Powering a garden room

This is the part garden-office buyers most often overlook, and it can add meaningfully to the budget. A fixed air conditioner cannot run off an extension lead trailed down the garden. Those degrade in sunlight, offer no proper earth-fault protection, and are a genuine hazard.

A garden room needs its own dedicated electrical supply: a sub-main cable run from the house consumer unit to a separate consumer unit inside the garden room, which then feeds the sockets, lighting and the air conditioning. That cable is normally steel wire armoured (SWA) cable, buried around 500mm deep, or 600mm where anyone might later dig, laid on sand with warning tape above it. The garden-room consumer unit has its own RCD protection so a fault out there cannot trip the whole house.

This is notifiable work under Part P of the Building Regulations. It must be done by a registered electrician, who issues an Electrical Installation Certificate confirming it meets the BS 7671 wiring standard. As a rough budget, a basic supply runs from about £600 to £1,000, a standard garden-office fit-out £1,000 to £1,800, and a full specification £1,800 to £2,500 or more, with long cable runs and trench digging able to push the total past £3,000. If you are installing both the supply and the air conditioning, it is often tidier and cheaper to have them coordinated on the same project.

Costs correct as of July 2026 and vary by cable run, groundworks and specification.

Sizing a glazed room

Do not undersize the unit. A garden room, and a sunny spare-bedroom office, need more cooling per square metre than an ordinary room because of all that glass and, in a garden room, the lightweight build.

As a starting point, a 2.5kW unit suits a space up to roughly 20m² and a 3.5kW unit up to about 30m², but those figures assume a normal room. A heavily glazed, sun-facing garden room can need noticeably more cooling for the same floor area, so it pays to size up rather than down and to have a proper survey rather than guess. An undersized unit runs flat out, never quite wins, and costs more to run for a worse result. Our guide to what size air conditioning you need explains how to work it out, and a good installer will calculate the heat load for your specific room, orientation and glazing.

Planning permission: two rules, not one

A garden office faces two separate sets of planning rules, and it is easy to satisfy one while breaching the other. Get both right before you build or install.

The air conditioning unit. In England, a reverse-cycle unit (one that heats as well as cools) can qualify as permitted development, under rules in force since 29 May 2025. A cooling-only unit cannot, because the rules exclude equipment used solely for cooling, so it generally needs a full planning application. The conditions include a unit no larger than 1.5 m³, limits on how many you can fit, and a noise limit of 37 dB(A) measured 1m from a neighbour's habitable-room window, assessed under the MCS 020-a scheme. This is another reason a reverse-cycle unit is the better choice. Read our full guide to air conditioning planning permission for the detail.

The garden room itself. As an outbuilding it has its own permitted-development limits: eaves no higher than 2.5m if it is within 2m of a boundary, an overall height no more than 4m for a dual-pitched roof or 3m otherwise, all outbuildings covering no more than half your garden, sited behind the front of the house, and used incidentally to the home rather than as a separate dwelling or sleeping space.

Flats, listed buildings and conservation areas are treated more strictly under both rules, and the devolved nations differ. Always check with your local planning authority before you commit.

On grants, a £2,500 air-to-air heat pump grant exists for England and Wales, but it is narrow: it applies to reverse-cycle units fitted by an MCS-certified installer to replace an existing fossil-fuel or electric heating system, one per property. It is not free air con, and comfort cooling alongside a boiler you are keeping will not qualify. Check GOV.UK and Ofgem for current availability before counting on it.

Grant and planning rules correct as of July 2026. Check GOV.UK, the Planning Portal and Ofgem for the current position before you commit.