Air cooler or portable air conditioner in the UK: how many degrees each drops, what they cost to run and which to buy

They are not the same machine and they do not do the same job. A portable air conditioner takes heat out of the room and pushes it outside through a hose, so it lowers the temperature of the whole room and takes moisture out of it at the same time. An air cooler, which is an evaporative cooler, sends nothing outside: it chills the air it blows and adds water vapour to it. A fan cools nothing at all; it moves air so that your skin evaporates sweat faster, which is why it feels like it works.

The reason this decision is different in Britain than almost anywhere else is that evaporative cooling runs on dry air, and British summer air is not dry. The trade itself puts the working threshold at about 60 to 65 per cent relative humidity. The driest July afternoon average in this whole guide is London at 60 per cent, and it is downhill from there. We would not buy an air cooler as the main answer to a British heatwave, and the table below is the reason: even at the best hour of the best month in the driest city on the list, the ceiling is 5.4 degrees, and a real machine only reaches part of its ceiling, only in the stream of air coming out of the grille.

Yes, all of them. A portable air conditioner works by taking heat out of the room air and dumping it into the hose, and if that hose is not going outside, the heat is going back into the room along with the waste heat of the compressor. A unit running with the hose coiled in the corner makes a room hotter, not cooler. This is not a preference or an installation tip: it is where the heat has to go.

And this is the part of the decision that is genuinely different in Britain. Most venting kits supplied with portable units are made for a sliding or tilt window, because that is what the rest of Europe and North America fit. A large share of British homes have side hung casement windows, where there is no straight sash to slide a panel into, and a fair number of period properties have sash windows, where the kit works better. Before you buy the machine, look at the window in the room you want to cool and work out where a 13 centimetre hose is going to leave. An air cooler has no hose at all, and for a rented flat where you cannot touch the window that is a real advantage, as long as you have read the table above and know what you are getting.

There are four, and all four come from the same thing: the machine is putting water into the air of your house. The first is that it does not lower the temperature of the room: it chills the stream of air coming out of the grille, and that sensation thins out as you move away from it. The second is the moisture it adds, which in a closed room comes back through its own intake: each pass cools a little less than the last, so you have to leave a window or a door open, which is the exact opposite of how you run an air conditioner.

The third is maintenance: a tank of standing water and a damp pad are somewhere things grow, so it gets emptied and dried when it is not in use and the filter gets rinsed. And the fourth is noise, because every bit of the cooling is produced by a fan pushing air through a wet pad: if the machine is quiet, it is not moving much air.

In a British house the second one matters more than it does in Spain. Our housing stock is the oldest in western Europe, and adding vapour to a room that is already at 65 per cent humidity is a different proposition from adding it to a room at 35 per cent. If there is condensation on your windows in winter, we would not put an evaporative cooler in that room at all.

No. A portable air conditioner is a plug in appliance: no planning permission, no notification, no qualified installer, and in a rented flat nothing that changes the building. It is the one form of air conditioning a tenant can use without asking anyone, which is most of why the question is asked so often.

What does need a qualified person is a fixed split system, the kind with a box on the outside wall. The refrigerant in it is an F gas, and UK law requires an F Gas certified engineer to install or service stationary units containing one. On top of that, an outdoor unit on a flat or an apartment almost always needs a planning application, because flats do not have the permitted development rights houses do and the equipment changes the appearance of a shared building. So the honest ranking for a British flat is: fan, then air cooler if you are in the dry half of the table above, then portable air conditioner, and a split system only if you own the place and are prepared for an application and a certified installer.

On 16 September 2026 we read the evaporative cooler listings returned by six different searches in the Amazon catalogue we track, and there were 40 distinct products. Of those forty: 23 give the tank size, 15 give the wattage and only 10 give the airflow in cubic metres per hour. Nine give both the airflow and the power draw, which are the two figures you need to compare one machine against another. Two declare the floor area they cover. And not one of the forty promises a number of degrees in its headline, which is the one good thing about all of this.

Airflow is the figure that decides and it is the one least often published. The tank size, which nearly all of them show, does not tell you how long it runs: it tells you how much fits. How long a fill lasts depends on the fan speed and on how dry the air is, because the tank is evaporating.