Here's the short version: a portable air conditioner costs roughly £200–500, arrives in a box and works tonight. A split system typically costs £1,500–3,000 installed and involves an engineer drilling through your wall. And yet, for most homeowners, the split is the better buy — by a distance. For renters and occasional users, though, the portable is genuinely the right call. Here's the fair fight.
What you're actually comparing
A portable unit is a self-contained box on wheels. Everything — compressor, fan, the lot — sits inside your room, and it pushes hot air out through a flexible hose you wedge into a window.
A split system puts the noisy, hot part (the condenser) outside on the wall, connected by slim pipes to a quiet indoor unit. Crucially, a modern split is a reversible air-to-air heat pump: it cools in summer and heats in winter, turning one unit of electricity into roughly three to four units of heat. That second job changes the maths completely.
The exhaust-hose problem
This is the bit portable manufacturers don't put on the box. Most portables sold in the UK are single-hose designs: they blow hot air out of the window, which lowers the pressure in the room, which pulls warm air back in — through the letterbox, under doors, around that badly sealed window the hose is poking out of. The machine is partly fighting itself.
Add the fact that the hose itself radiates heat back into the room, and a portable rated on paper for a decent-sized space often struggles with a warm bedroom on a genuinely hot evening. It will take the edge off. It won't give you the crisp, set-it-to-19-and-forget-it cold a split delivers.
Noise, and why it matters more than you think
A portable is a compressor in your bedroom. Typical units run at roughly 50–65 decibels — somewhere between a lively conversation and a vacuum cleaner. Some people sleep through it; many don't, which is awkward given that hot nights are exactly when you bought it.
A split's indoor unit typically runs at around 19–30 decibels on its low setting — quiet enough to sleep next to. The compressor is outside (worth a read of our guide on AC noise and neighbours if you share a party wall). For sleep, this is the single biggest difference between the two.
The honest side-by-side
| Portable | Split system | |
|---|---|---|
| Upfront cost | Roughly £200–500 | Typically £1,500–3,000 installed (one room) |
| Installation | None — plug in tonight | Professional install, usually done in a day |
| Cooling on a hot day | Takes the edge off | Properly cold, holds a set temperature |
| Noise where you sit | Roughly 50–65 dB, in the room | Roughly 19–30 dB indoors |
| Efficiency | Low — hose losses eat into it | High — roughly 3–4 units of heat or cooling per unit of electricity |
| Heats in winter | No (or inefficiently) | Yes — it's a heat pump |
| Landlord's permission | Not needed | Needed (it's fixed to the building) |
| Stays with the home | No | Yes — a permanent fixture |
On running costs: a portable working flat out on a hot day can cost more per hour than a split cooling the same room, because so much of its effort leaks back in through the hose. Over a few summers of regular use, the gap adds up — we've broken this down properly in our guide to air conditioning running costs.
When a portable is genuinely the right choice
We'd rather be straight about this than pretend splits win every time. Buy a portable if:
- You rent. A split is fixed to the building and needs your landlord's blessing; a portable moves out when you do. For most tenants this settles it.
- You need cooling this week. Heatwave on, baby not sleeping — a portable works tonight.
- You'll use it a handful of days a year. If it lives in a cupboard for eleven months, £300 is proportionate and £2,500 isn't.
- You're testing the water. Plenty of people run a portable for one summer, decide cooled sleep is non-negotiable, and upgrade.
When the split earns its price
If you own your home and you'll want cooling most summers, the split case is strong. It cools properly and quietly, and then — the part that usually swings it — it heats efficiently through winter. On the right electricity tariff, that can work out cheaper per unit of warmth than a gas boiler, though the sums depend on your rates and how you run it.
A multi-split covering three or four rooms typically runs somewhere around £3,500–7,000, and pairing either with solar can cut the running cost further still. If you're weighing up the numbers, start with our full breakdown of what air conditioning costs in the UK.
The bottom line
Renter, occasional user, or need it tomorrow: buy the portable, seal the window kit properly, and don't expect miracles on the hottest nights. Homeowner planning to stay put: the split costs several times more, and if you'll use it year-round it earns the difference — quieter, colder, cheaper to run for the same cooling, and heating your home all winter.
If you're leaning towards a split and want a sanity check on price for your actual rooms, you can get a free quote — we'll match you with one vetted local installer, not a list of firms competing for your phone number.