Millions of us now work from home, and plenty of us do it in the least comfortable room in the house: the box room nobody else wanted, a loft conversion, or a garden office at the end of the lawn. None of these spaces were designed for eight hours of occupation with a computer running, and in a warm spell they can be genuinely hard to work in by early afternoon. This guide covers why home offices overheat worse than other rooms, how the right unit gets sized, the wiring question every garden-office owner should ask, and why the same unit earns its keep in January too.
Why home offices overheat worse than any other room
Three things gang up on a home office. First, small volume: a box room holds far less air than a living room, so the same heat input pushes the temperature up faster. Second, you and your equipment add heat all day. A desktop computer, a couple of monitors and a warm human are effectively a small heater that never switches off, often in a room with a single openable window. Third, location: loft conversions sit directly under the roof, which the sun works on from morning to evening, and garden offices are typically lightweight timber buildings with generous glazing and modest insulation. They warm up fast and hold onto it.
A fan helps while the air in the room is still cooler than you are. Once the room itself is hot, a fan is just stirring warm air around, which is roughly the point most home workers give up and decamp to the kitchen table.
What size unit a home office actually needs
Less than you might think. A box room or a modest garden office usually only needs the smallest unit in an installer's range, and even a sun-baked loft office rarely needs to go much bigger. Oversizing isn't a safety margin, either: an oversized unit cools the air quickly without dehumidifying it properly, and cycles on and off more than it should. A decent installer sizes the unit on a survey, taking the glazing and sun exposure into account rather than guessing from floor area, so be wary of any firm that quotes a size without seeing the room.
On price, a single-room split is at the affordable end of air conditioning, though an awkward pipe run pushes the figure up and loft conversions can be fiddly. Our guide to air conditioning costs breaks down what drives the number. If you're weighing a split against a cheap portable unit, one thing matters more in an office than anywhere else: noise. A portable puts the compressor in the room with you, which is no fun when you're on calls all day, while a split puts the noisy part outside on a wall. There's a fuller comparison in our split vs portable guide.
The garden office power question
Before anything else, find out how your garden office is fed. Done properly, it's supplied by armoured cable buried in the garden, running back to its own circuit in the house's consumer unit. Done less properly, and plenty are, it runs off an outdoor socket or a lightly rated spur, which is fine for a laptop and a lamp but not something to hang an air conditioner on.
A split unit's electrical draw is modest, but it runs for hours at a stretch, so the supply needs to be sized for it. If you don't know what your cable can carry, ask a qualified electrician to check before anyone quotes for a unit. And that is as far as a homeowner should take it: finding out how the office is fed and passing that on to the installer is genuinely useful, but touching the cable, the consumer unit or anything on the fixed wiring is not a DIY job under any circumstances. Our guide to whether your home electrics can handle air conditioning covers the house side in more detail.
| Job | Who should do it |
|---|---|
| Finding out how the office is fed; shading, ventilation, cleaning dust filters with the unit off | You |
| Assessing the supply cable, the consumer unit, or adding a circuit | A qualified electrician |
| Installing, servicing or repairing the split system itself | An F-Gas certified engineer |
It heats in winter too, so it works year-round
Here's the part most people don't know: a modern split system is a reversible air-to-air heat pump. Run in reverse in winter, it moves heat indoors rather than generating it from scratch, so you typically get several units of heat for every unit of electricity it uses. The exact figure depends on the unit and how cold it is outside, but a plug-in fan heater manages exactly one, every time. Whatever your tariff, heating a small, well-sealed office this way costs a fraction of running the fan heater under your desk. For a garden office that's freezing in January and roasting in July, one unit fixes both problems for the same money.
One honest caveat: air-to-air heat pumps aren't covered by the Boiler Upgrade Scheme, which is for heat pumps that heat your radiators and hot water. So there's no grant, but the install cost is modest to begin with.
Cheap things worth doing first (or as well)
- Shade the glass from outside if you can. An internal blind helps, but stopping the sun before it hits the window works far better: an awning, an external blind, or even carefully placed planting.
- Ventilate early. Open everything first thing while the outside air is cool, then shut windows and blinds as the day warms up.
- Get heat out of the room. A laptop runs cooler than a tower PC, turning monitor brightness down helps a little, and anything that runs hot, like routers and printers, can often live elsewhere.
These buy you a few degrees. On a genuinely hot week they won't be enough on their own, but they cost little and make whatever cooling you do install work less hard.
Getting it installed
Whoever fits the system must be F-Gas certified. That's a legal requirement for anyone handling refrigerant, not a nice-to-have, and it applies for the life of the unit: the refrigerant circuit and the sealed electrical parts are strictly engineer territory, and the most you should ever do yourself is clean the dust filters with the unit switched off. If you'd like a realistic figure for your office, tell us about the room, or the garden office and how it's fed, and we'll match you with a vetted local installer for a free survey and a no-obligation quote. Start with a quick estimate.