Do evaporative air coolers work in Europe? The wet-bulb answer

Updated August 30, 2026 · Claude AC · 2 sources cited

Contents (7)

One machine, one hard physical limit
What that means in European air
The running cost is genuinely small
The conditions you have to accept
A category with no energy label
Where it belongs in a European cooling plan
Frequently asked questions

The listing looks like an air conditioner. Grille, remote, a « 3-in-1 » badge, a price around €90, and a photograph of somebody sleeping peacefully. Every European summer it sells in volume to people who have just spent a fortnight sleeping badly. What arrives is an evaporative air cooler: a fan, a small pump, a water tank and a wet pad. There is no refrigerant circuit and no compressor, so it cannot do what an air conditioner does. Whether it will help you at all depends on one number that almost nobody checks before buying — the wet-bulb temperature of the air outside your window.

One machine, one hard physical limit

An evaporative cooler draws air through a soaked pad. Water evaporates into that air, and the energy required for the phase change — roughly 2,260 kilojoules per kilogram of water — is taken out of the air itself, which leaves colder and considerably wetter. The floor of the process is the wet-bulb temperature. No direct evaporative machine can supply air below it, and a well-maintained unit closes about 70 % to 85 % of the gap between the ordinary dry-bulb temperature and the wet-bulb. The psychrometrics are set out in full in our explainer on how evaporative cooling works.

Two consequences follow, and between them they are the whole story. The machine adds moisture to a room instead of removing it, the exact inverse of what a refrigerated system does. And its usefulness is governed by how dry the incoming air is, not by how hot it is: a 36 °C afternoon in the Ebro valley is far friendlier terrain than a 30 °C afternoon in Rotterdam.

What that means in European air

The table takes typical hot-afternoon conditions for a spread of European climates — indicative figures, not climate normals — and works out the wet-bulb limit and the air a good pad would actually deliver at 80 % effectiveness.

Typical hot afternoon	Outdoor air	Wet-bulb limit	Air delivered	Verdict
Inland Iberia (Madrid, Córdoba)	35 °C, 20 % RH	19 °C	about 22 °C	Excellent — a genuine alternative
Ebro valley (Zaragoza)	36 °C, 22 % RH	21 °C	about 24 °C	Excellent
Pannonian and Danube plains	34 °C, 35 % RH	23 °C	about 25 °C	Worthwhile on dry days
Paris or Berlin heat spike	33 °C, 38 % RH	22 °C	about 25 °C	Worthwhile, not transformative
London, dry hot day	32 °C, 40 % RH	22 °C	about 24 °C	Marginal
Athens, coastal afternoon	33 °C, 42 % RH	23 °C	about 25 °C	Marginal
Po valley (Milan, Bologna)	33 °C, 55 % RH	26 °C	about 27 °C	No — adds humidity for little gain
Adriatic and Tyrrhenian coasts	32 °C, 55 % RH	25 °C	about 26 °C	No
Muggy night, North Sea coast	29 °C, 60 % RH	23 °C	about 24 °C	No

Read the right-hand column and the European verdict writes itself. Evaporative cooling is a serious technology in interior Iberia and on the dry continental plains, a marginal one on the Atlantic fringe, and a mistake almost anywhere the sea sets the humidity. It is also seasonal within a single place: the same flat in Spain that loves a cooler through a dry July afternoon gains very little from it during a humid easterly spell.

One caveat the table cannot carry. The fourth column is the temperature of the air leaving the machine, not the temperature the room settles at. A cooler moving a few hundred cubic metres an hour into a 25 m² living room produces a cool draught where you sit and a modest drop in the room average — which is why personal-sized units are best understood as directional comfort devices rather than room coolers.

The running cost is genuinely small

There is no compressor, so consumption is a fan and a pump: roughly 60 to 250 W for domestic machines, against 700 W to 1.2 kW for a portable air conditioner of the size people buy. Put a European summer on it. A 150 W cooler running eight hours a day for sixty days uses about 72 kWh — near €18 at an indicative €0.25 per kilowatt-hour. A single-duct portable drawing 1 kW over the same hours uses roughly 480 kWh, or about €120, and that is before the infiltration penalty measured in our comparison of portable versus split air conditioners. The gap is real, and it is the honest argument for the category — provided the machine does anything in your climate at all. Water is the second consumable and stays modest: one to two litres an hour when the unit is working properly. A cooler that barely drinks on a humid day is not faulty; that is the physics reporting that the air will take no more moisture.

The conditions you have to accept

A window stays open. An evaporative cooler is a one-pass machine: it must be fed relatively dry air and the humid air it produces has to leave. Seal the room as you would for an air conditioner and within an hour you have a humidifier with a fan attached.
Humidity rises indoors. That is the mechanism, not a defect. In a room that is already damp — a ground-floor flat, a northern coastal town — it is a poor idea regardless of the temperature.
It cannot dehumidify. If your complaint is the sticky, close feeling rather than raw heat, the machine you need is the opposite one, as our comparison of a dehumidifier and an air conditioner explains.
Daily hygiene. A warm tank of standing water with an organic pad in it is a microbial culture. Empty and rinse the tank when the machine is not in use, dry the pads periodically, and replace cellulose pads when they scale up — hard European tap water is what kills them.

A category with no energy label

Splits and portables carry the EU energy label because they meet the definition of an air conditioner in Commission Regulation 206/2012. A pure evaporative cooler cannot function without water, falls outside that definition, and therefore has no EER, no SEER and no A-to-G class at all. Any efficiency class printed on such a listing refers to nothing comparable, a distinction worth holding onto alongside the traps described in our guide to reading the EU energy label.

What to read instead, in order: air delivery in m³/h — evaporative cooling replaces room air continuously rather than recirculating it, and a workable rule is to turn the room volume over about twenty times an hour, so a 12 m² bedroom with a 2.5 m ceiling wants roughly 600 m³/h. Then pad type (rigid cellulose honeycomb outlasts loose aspen wool), tank capacity against the hours you want unattended, and sound in dB(A), since a machine that must run flat out to be useful is one you will hear all night.

Where it belongs in a European cooling plan

Order the options by cost and by what they can achieve. Shutters, external shading and night flushing come first everywhere and cost nothing to run — the sequence is in our guide to cooling a European home without air conditioning. A fan comes next, and in humid weather it beats an evaporative cooler outright, because moving air over skin works whatever the dew point is doing. The cooler earns third place, in dry inland heat, where it delivers a real drop for a fifth of the electricity of refrigeration. Beyond that — a top-floor Mediterranean bedroom, three weeks of tropical nights — only a refrigerated machine will do, and the question becomes whether you can get consent for a split system.

Frequently asked questions

Do air coolers work in the UK?

Only marginally, and least of all when you most want them. British heat comes in two flavours: dry, continental-drawn spikes where a cooler can take a few degrees off the air it blows, and muggy Atlantic warmth where the wet-bulb is close to the air temperature and the machine has almost nothing to work with. Since the sleepless nights in the United Kingdom are overwhelmingly the second kind, a fan is the better purchase and a portable air conditioner the better machine.

Is an air cooler the same thing as a portable air conditioner?

No, and confusing the two is the commonest regret in this category. A portable air conditioner has a compressor and a refrigerant circuit, needs a hose out of a window, removes moisture and can hold a setpoint. An evaporative cooler has a fan and wet pads, needs no hose, adds moisture and cannot hold a temperature. They differ by a factor of five to ten in both price and power draw.

Does putting ice in the tank make a difference?

Very little, and not for long. The cooling you feel comes overwhelmingly from evaporation rather than from the water temperature — and colder water evaporates more slowly, which works against the effect you are trying to create.

Will an air cooler make my room damp or mouldy?

Used as designed — dry air in, window open, tank emptied — no. Used as people are tempted to use it, in a closed bedroom over successive humid nights, it raises humidity in a poorly ventilated room, which is precisely the condition dampness and mould need.

What size of cooler do I need for a bedroom?

Work from volume, not floor area: multiply floor area by ceiling height and look for roughly twenty times that figure per hour — about 600 m³/h for a small bedroom, 1,200 to 1,500 m³/h for a living room. Personal units are routinely sold for rooms three times larger than they can serve, which is why buyers conclude the technology does not work when what failed was the arithmetic.