Mobile air conditioning units, evaporative "air coolers" and fixed split systems compared honestly — what each one really does in a UK heatwave, what it costs to run, and when a portable genuinely makes sense.
Every hot spell, the same thing happens across Wiltshire: mobile air conditioning units sell out in Swindon and Salisbury within days, and a week later half the buyers are wondering why their bedroom is still 27°C at midnight. We install fixed systems for a living, so you'd expect us to favour them — but the case below isn't sales talk. It's physics, decibels and pence per hour. There are situations where a portable is the right call, and we'll tell you exactly what they are.
These are real air conditioners: they have a compressor and refrigerant, and they do remove heat. The problems are practical. The hot air has to go somewhere, which means a fat exhaust hose wedged out of a window — usually through a gap that lets warm air straight back in. Most models are single-duct, which creates a quiet flaw few buyers know about: the machine blows air out of the room, so replacement air gets sucked in through every gap, door and floorboard — and that replacement air is warm outside air. You're cooling the room and reheating it at the same time.
Then there's the noise. The whole compressor sits inside the room with you, so expect 60dB or more — roughly the level of normal conversation, right next to your bed, all night. And in a proper heatwave, when the outside air climbs above about 28°C, most portables struggle to keep up at all. The one time you desperately need it is the one time it can't cope.
Cheap, quiet, and heavily advertised every June — but an air cooler is not an air conditioner. It's a fan blowing air over water. Evaporation absorbs a little heat, which works nicely in a dry climate like southern Spain. In a muggy British July, the air is already loaded with moisture, so almost no evaporation happens. What you get is a slightly damp breeze and a stickier room. If you see "no hose needed" on a cooling product, that's your clue: it isn't removing any heat from the room.
A wall-mounted split system puts the noisy compressor outside and leaves only a whisper-quiet fan unit indoors — typically 19–26dB, quieter than a library. Because the heat is rejected outside through sealed pipework rather than a hose out of the window, it cools genuinely and quickly, and it keeps working through the hottest days. Every unit we install also runs in reverse as an efficient heat pump, giving you cheap heating in winter, and a professionally installed system adds appeal and value to your home. The catch is obvious: it costs more upfront and needs a professional installation.
Here's the comparison that surprises people. Assuming electricity at around 28p/kWh:
| Type | Typical power draw | Cooling delivered | Cost per hour |
|---|---|---|---|
| Portable unit | ~1.0kW | Weak — much of it lost through the hose and infiltration | ~28p |
| Evaporative air cooler | ~0.06kW | Effectively none in humid UK air | ~2p |
| Fixed split system (2.5kW) | ~0.7kW | Strong — full rated cooling, room reaches temperature and holds it | ~20p |
Read that again: the fixed system costs less per hour than the portable while delivering far more actual cooling. Modern inverter splits also throttle right down once the room is at temperature, so the real-world average draw is often half the rated figure. Full workings are in our running costs guide.
Upfront price is only half the story. Take a bedroom used through a typical British summer — say 300 hours of cooling a year — and add winter heating for the fixed system (which portables can't do at all):
| Portable unit | Fixed split system | |
|---|---|---|
| Purchase / installation | £500 (often replaced once in 5 years: +£500) | £1,800 installed |
| Cooling electricity (5 yrs) | ~£420 | ~£300 |
| Winter heating savings vs plug-in electric heater | — | −£400 or more |
| Comfort delivered | Partial, noisy | Full, near-silent |
| Realistic 5-year cost | ~£1,400+ | ~£1,700 — with heating, often less |
Once you factor in the heating mode offsetting an electric heater in a home office or spare room, the fixed system frequently works out cheaper over five years — while actually doing the job the portable only gestures at.
Outside those cases, if you own your home and you're reaching for air conditioning more than a handful of days a year, a fixed system is the honest recommendation — quieter, colder, cheaper to run, and useful twelve months a year instead of two.
If you're weighing up a decent portable against a fixed system, get a real number before you decide — it's often closer than you think. Send us a message with your town and the room you want cooled, and we'll come back with a fixed, no-obligation price for a properly installed split system, anywhere in Wiltshire.
Most portables are single-duct machines: they blow hot air out of the window but pull warm replacement air back in through every gap and doorway, and heat leaks back through the hot exhaust hose itself. Above about 28°C outside, many simply can't remove heat faster than it returns — so the room never gets properly cool.
No. Evaporative air coolers are fans blowing air over water — they add moisture rather than removing heat. In the UK's already-humid summer air they achieve very little. Only refrigerant-based air conditioning actually lowers the room temperature.
Technically yes — an F-Gas engineer can recover the refrigerant and reinstall it elsewhere. In practice it's rarely worth it: removal, new pipework and recommissioning cost close to a fresh install, and a fitted system adds appeal to the home you're selling, so most owners leave it in place.
Tell us your town and which rooms you'd like cooled or heated — someone from our local team will come back to you as soon as possible with a fixed price.
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