Evaporative Air Coolers: How They Work in UK Conditions

An evaporative air cooler is a plug-in appliance that cools air with water rather than refrigerant. It draws warm air from the room through water-soaked pads, lowering the air's temperature naturally before releasing it back into the room¹. There is no compressor, no refrigerant gas and no installation: most domestic models are described by their sellers as plug-and-play, needing only water in the tank and a nearby power socket¹.

The catch, and it is a big one for a damp country, is that the cooling comes from evaporation, and evaporation needs dry air. Makers themselves state that these coolers are ideal for dry or moderately humid climates and that in very humid conditions cooling performance may be reduced¹. On a dry heatwave day a good unit takes the edge off a living room for pennies an hour; on a muggy, overcast day it does little a fan could not do. This page explains the physics in plain terms, where the UK climate helps and hinders, what the tanks, the running costs and the hygiene rules involve, and how the three iKool models sold in the UK compare.

How evaporative air coolers work

An evaporative air cooler is a simple machine at heart: a water tank, a wick or pad that soaks up water, and a fan that pulls room air through those wet pads. As the air passes through, some of the water evaporates into it, and evaporation absorbs heat, so the air coming out of the front of the unit is cooler than the air that went in¹. The same principle is at work anywhere water dries: guidance on garden water features notes that water has a natural cooling effect through evaporation, and even a small pond can lower surrounding air temperatures⁵.

This is why the appliance needs no refrigerant circuit. A refrigerant system, whether a dehumidifier or an air conditioner, has an evaporator: a low-temperature heat exchanger where refrigerant enters as a cold liquid, absorbs heat by evaporating at low pressure, and leaves as a vapour⁶. An evaporative cooler borrows only the name of that process. The water itself is the working fluid, thrown away into the room as humidity rather than recycled through a sealed circuit, and that single difference drives everything else on this page: the low running cost, the low price, the absence of installation, and the hard limit in damp weather.

What the unit delivers is a stream of cooler, damper air, not a chilled room. Independent summer energy guidance describes air coolers as using water to slightly cool air, more effective than fans in dry conditions³. That word "slightly" is honest: the appliance lowers the temperature of the air passing through it, and how much that cools the room depends on how dry the air is, how much air flows through, and whether damp air can escape.

These coolers humidify the air rather than use refrigerant

Every litre of water an evaporative cooler turns into vapour goes into the room's air. That is not a side effect; it is the mechanism. The heat that evaporates the water is taken from the air, so the air cools, but the room's humidity rises in exchange. In a dry environment the maker describes this as beneficial, adding welcome moisture to parched summer air¹. In a sealed British living room on a day when the air is already moist, there is little room left in the air for more vapour, and the cooling stalls.

The contrast with refrigerant appliances is worth understanding, because it explains why the two technologies behave so differently. A refrigerant dehumidifier draws moist air in and passes it over cold coils, where the moisture condenses and collects in a tank or drains away: it removes water from the air⁷. An evaporative cooler does the exact opposite, adding water to the air. Run side by side they would fight each other.

The moisture itself is not a hazard to a building in normal use, but it is worth knowing that buildings already manage moisture by evaporation. Official guidance on traditionally constructed buildings explains that the fabric of such a building needs to "breathe", so that moisture within walls, from driving rain or condensation, can be released through evaporation⁸. A cooler running for hours in a poorly ventilated room is adding to the moisture load that the building then has to shed, which is one reason the running advice in the next sections always comes back to airflow.

How well evaporative cooling suits the British weather

The UK is not Arizona, and that shapes what these appliances can do here. The starting position is that British summers are warming into something where cooling demand is real: the Climate Change Committee's 2026 Independent Assessment of UK Climate Risk suggests almost a quarter, 22%, of UK buildings would need active cooling in a future with 2°C of warming⁴. Yet air conditioning remains rare: only 4% of households in England have it⁹. Most homes face hot spells with fans and open windows, which is exactly the gap evaporative coolers sit in.

The climate itself is mixed news for the technology. Air temperatures fluctuate between -5°C and 25°C for at least 95% of the year for most UK homes¹⁰, so the hot, dry days when an evaporative cooler shines are a minority of the year, but they are the days that matter. The UK also has some of the most poorly insulated homes in Western Europe, losing heat on average three times faster than homes in Germany or Norway¹¹, and poorly insulated, lightweight homes tend to overheat quickly in sun before cooling fast at night. That swing can suit an appliance that takes the edge off a hot afternoon.

The bigger problem is awareness rather than physics. A London call for evidence found that while 64% of consumers recognise that energy efficiency measures help keep homes warmer "at least quite a bit", fewer than half, 42%, understand that these same measures can help keep homes cool in summer¹². Households that shade, insulate and ventilate well need less of any cooling appliance; households that do not will ask an evaporative cooler to fight the sun alone, and it is not built for that. In our mild climate, passive ventilation, with warm air rising through the building and fresh air coming in through a buffer space such as a south-facing conservatory, is usually appropriate as a first line of defence¹³.

Where does that leave the cooler? It helps most in the dry, sunny spells that increasingly bookend British summers, in rooms with some airflow, and for people who want relief without the cost of air conditioning. It falls short in humid heat, in sealed rooms, and as a whole-house solution. Air-to-air heat pumps, which cool as well as heat, are described as a highly effective low-carbon solution for heating and cooling UK homes, particularly smaller properties with electric heating, but they remain uncommon in the UK¹⁴, so for now most households choose between fans, coolers and portable or fixed air conditioning.

Comparing coolers, fans and air conditioning

The three options sit on a ladder of cost and effect. A fan moves air without cooling it at all; it helps because moving air carries heat away from your skin, and it is far cheaper to run than air conditioning⁵. An evaporative cooler is a fan plus water: it moves the air and slightly lowers its temperature, doing more than a fan in dry conditions³. Air conditioning actually pumps heat out of the room using a refrigerant circuit, and it is the only one of the three that can hold a room at a set temperature regardless of humidity.

The running costs follow the same ladder. A typical portable air conditioner of 1,000 to 1,500W costs around 26 to 39p an hour to run, roughly 14 to 20 times more than a fan³. An air cooler sits near the fan end: one industry cost comparison published in May 2026 listed an air cooler at 75W, costed at 11p an hour and £1 a day on one tariff, and 14p an hour and £1.25 a day on a higher rate². Against a portable air conditioner at 26 to 39p an hour, the cooler's electricity use is a small fraction.

Two further points of comparison matter. Portable air conditioners need to be properly vented to the outside using a special fitting for the window, and a vent simply put through an open window lets heat back in¹⁵; an evaporative cooler has no hose at all. On the other hand, refrigerant cooling is unaffected by humidity, whereas a cooler's output collapses in muggy weather. Makers state that evaporative coolers use significantly less electricity than traditional air conditioning and do not require refrigerants¹, and that claim is consistent with the published figures above; what they cannot do is dehumidify, cool a whole home, or hold a temperature on a humid night.

What a cooler does with open windows

This is the point that most surprises people who have used air conditioning. A refrigerant cooler works best in a sealed room, because every bit of cool air it produces is precious and the heat it extracts has to go somewhere through a hose. An evaporative cooler works the opposite way: it adds moisture to the air, and if that moist air has nowhere to go, the room's humidity climbs until the water in the pads can no longer evaporate into it and the cooling stops.

So the practical pattern is a window or door open, at least slightly, on the far side of the room from the unit. Fresh, drier air flows in, the cooler treats the air passing through it, and the dampened air drifts out. This is not a maker's marketing claim; it follows from the physics described above, and it is echoed in the wider ventilation guidance for buildings: natural ventilation carries lower embodied carbon than mechanical systems¹⁶, and passive approaches are usually appropriate in the UK's mild climate¹³.

The contrast with a portable air conditioner is worth restating because it is the commonest setup mistake. Independent guidance is explicit that portable units "need to be properly vented to the outside using a special fitting for the window. If the vent is just put through an open window, heat will leak back in"¹⁵. An evaporative cooler has no such requirement: it is plug-and-play, needing only water in the tank and a nearby power socket¹. If you are moving from one technology to the other, the habits have to move too: sealed room for the air conditioner, airflow for the cooler.

Tank capacity, refilling and running time

Every evaporative cooler holds its water in a tank inside the unit, filled from a tap or jug. How long a tank lasts depends on the tank's size, the fan speed and above all the dryness of the air: the drier the day, the more water evaporates and the better the cooling, but also the sooner the refill. Makers do not publish a litres-per-day figure for domestic coolers, so treat any refill claim as a guide rather than a specification. What the maker of the iKool-25 Plus does say is that its tank provides extended cooling without frequent refills¹.

There is no UK standard for how long a domestic cooler's tank should last, and no independent test data in the public domain, so the honest answer to "how long does a tank last" is: until the water runs out, which you will learn quickly for your own room and weather. As a sense of scale for how much water appliances can quietly consume, guidance on washer-dryers notes they use a continuous run of cold mains water to condense vapour during drying¹⁷; an evaporative cooler is far thirstier than nothing but far more modest than that, and topping it up is part of using it.

Hygiene matters more than convenience here. The one practice worth carrying over from other tanked appliances comes from dehumidifier guidance: empty the water tank after each use and before moving the unit⁷. Standing water in a warm appliance between uses is the condition to avoid, and the cleaning instructions in the maker's manual exist for the reason covered in the safety section below.

Carrying and siting your cooler around the home

Portability is one of the technology's genuine strengths over fixed air conditioning. There is no outdoor unit, no pipework and no fitter: the appliance is filled, plugged in and switched on¹. The iKool-25 Plus is described by its maker as easy to move and position as needed¹, and the larger iKool-80 Plus as easy to move and position using wheels¹, so even the biggest model in the range is designed to travel between rooms rather than be fixed in one.

Positioning follows from how the unit works. It wants a supply of warm, drier air to draw in, a clear path for the cooled air across the people in the room, and, as above, somewhere for the moistened air to go. Near an open window on the fresh-air side of the room, blowing across the room towards an open door or window on the other side, is the arrangement the physics rewards. Pushed into a sealed corner, the same unit will dampen the air and deliver little cooling.

The practical rhythm for most households is one cooler moved to wherever the people are: a living room through the afternoon, a bedroom for the evening. That is a different proposition from whole-home cooling, and it is the honest limit of the category. A single portable appliance of any kind cools a space, not a house, and an evaporative cooler's space is smaller again on humid days.

Choosing the right model for home or workplace

The range sold in the UK spans both settings. The maker describes its domestic evaporative air coolers as perfect for living rooms, bedrooms, conservatories, home offices, or anywhere you need cost-effective cooling¹. The smallest model in the range, the iKool-25 Plus, is described as perfect for residential use¹, while the middle model, the iKool-50 Plus, is listed as a domestic and commercial product¹, and the largest, the iKool-80 Plus, sits on wheels for moving around larger spaces¹.

The pattern is the usual one: smaller units for rooms, larger and wheeled units for open-plan or business settings. A shop floor, a small office or a village hall has the high ceilings and air volume that make a bigger fan and tank worthwhile, and often has doors opening and closing, which suits a technology that wants airflow. A bedroom or home office wants the opposite: a compact unit, low power draw and a tank that lasts the evening.

For a household weighing this against other options, the setting matters as much as the model. A conservatory on a sunny afternoon is close to the ideal case for the technology: hot, often dry air, plenty of volume, doors to open. A north-facing bedroom on a humid night is close to the worst case, and no size of evaporative cooler fixes that.

Comparing the iKool 25 Plus, 50 Plus and 80 Plus

The domestic evaporative coolers sold in the UK by Cool Easy are the iKool-25 Plus, iKool-50 Plus and iKool-80 Plus. All three use the same evaporative technology, drawing warm air through water-soaked pads to lower its temperature before releasing it into the room¹. What differs is the intended setting, the portability arrangement and the price.

The prices need explaining, because the maker's own page shows different figures for the same models. The iKool-25 Plus is listed at £52.00 including VAT, against a stated High Street price of £199.99 including VAT¹. The iKool-50 Plus appears at £30.00 including VAT in one place and £264.99 including VAT in another, against a High Street price of £294.99 including VAT¹. The iKool-80 Plus appears at £169.00 including VAT in one place and £425.99 including VAT in another, against a High Street price of £594.99 including VAT¹. These figures differ within the maker's own listing, so the prices are those published on 23 September 2026 and the current page should be checked before buying; the £30.00 figure for the 50 Plus in particular looks out of step with the rest of the range.

Beyond size and price, the maker's descriptions are thin on numbers: no airflow rates, no tank capacities in litres, no cooling output in kW are published for these models. That absence is itself useful information. An evaporative cooler cannot be specified the way an air conditioner can, because its output depends on the weather, so a buyer is choosing on size, portability and price rather than on a rated cooling capacity.

Purchase price and running costs of an evaporative cooler

On purchase price, this is the cheapest category of powered cooling on the market. The range above runs from £52.00 including VAT for the iKool-25 Plus to £169.00 including VAT for the iKool-80 Plus in the maker's lower listings, with higher figures also shown on the same page as set out above¹. Even taking the higher figures, an evaporative cooler costs less than most portable air conditioners and a fraction of a fixed split system, and unlike both it needs no installation cost at all: no fitter, no vent kit, no outdoor unit¹.

Running cost is where the category earns its place. An air cooler was listed at 75W in a May 2026 industry cost comparison, costed at 11p an hour and £1 a day on one tariff, and 14p an hour and £1.25 a day on a higher rate². Compare that with a typical portable air conditioner at 1,000 to 1,500W, costing around 26 to 39p an hour, roughly 14 to 20 times more than a fan³, and the gap is an order of magnitude. Makers state that evaporative coolers use significantly less electricity than traditional air conditioning and do not require refrigerants¹, and the published figures bear that out.

Two cautions keep the comparison honest. First, the cooler's output is weather-dependent, so the low running cost buys less cooling on the days when you most want it, if those days are humid. Second, the comparison with fixed air conditioning is not like for like: portable units use 30 to 50% more electricity than fixed systems¹⁵, and a fixed system cools regardless of humidity. The evaporative cooler is cheap because it does less, and for many UK households in a dry spell, less is enough.

Leaving a cooler on safely through the night

The safety question for these appliances has two parts: electricity and water. Electrically, a 75W appliance is a modest load, and nothing in the UK guidance on portable electrical appliances singles coolers out. The water side is where the documented risk sits. Summer energy guidance on air coolers is blunt: "make sure you follow the instructions to avoid the risk of Legionnaires' disease."³ Legionella bacteria breed in warm, standing water, and an appliance that holds a tank of it and blows air through it is exactly the kind of device those instructions exist for. Emptying the tank after use and before moving the unit, as advised for tanked appliances such as dehumidifiers⁷, and following the maker's cleaning schedule, is the practical response.

On overnight running, there is no UK guidance specific to evaporative coolers, so the honest position is built from the rules for comparable appliances. Guidance for dehumidifier owners says to avoid running overnight or while away from home unless the manufacturer specifies the appliance is safe for unattended use⁷. The same caution runs through portable heating guidance: it is recommended not to use a portable heater overnight, and never to leave one unattended while in use or while asleep¹⁸. Belfast City Council's winter advice makes the parallel point for electric blankets, which can be dangerous if left on overnight unless they have a safe all-night setting¹⁹.

None of those rules is about coolers, and none of them forbids overnight use of a well-maintained unit whose maker permits it. But the pattern across UK safety guidance is consistent: water-bearing and portable electrical appliances are run attended by default, and unattended running is something a manufacturer has to specifically allow. If a cooler is used overnight, the conditions that matter are clean water, a tank that is not days old, and a maker's manual that says the unit may run unattended.