The short answer
An evaporative air cooler blows air through a wet pad so that evaporating water cools it. It uses little electricity and needs no hose or installation, but it isn't air conditioning, adds humidity and does little on humid days.
On this page
Evaporative coolers look like tower fans or small portable air conditioners and are often sold alongside them. Inside, though, there's no refrigerant and no compressor, just a fan, a water tank, a pad and usually a small pump. How well one works depends mostly on how dry the air is.
How evaporative cooling works
Water needs heat to evaporate, and it takes that heat from the air passing through the wet pad. The air comes out cooler but carrying more moisture. It's the same effect that makes wet skin feel cold in a breeze.
The drier the air, the more water evaporates and the bigger the drop in temperature. When the air is already humid, little water can evaporate, so the cooling effect shrinks and the extra moisture can make a room feel clammy.
Unlike an air conditioner, a cooler doesn't move heat out of your home. It trades some of the air's heat for moisture, which is why it needs fresh air coming in and moist air getting out to keep working.
Air cooler or air conditioner
If a product has a water tank you fill, no exhaust hose and no outdoor unit, it's an evaporative cooler rather than an air conditioner.
| Evaporative cooler | Air conditioner | |
|---|---|---|
| How it cools | Evaporates water into the air | Moves heat outside |
| Humidity | Adds moisture | Removes moisture |
| In a closed room | Stops helping as humidity builds | Works best |
| Power use | Low, a fan and a pump | Higher |
| Upkeep | Refill the tank, clean the pad | Clean the filters, regular service |
In a UK home
- UK air is often fairly humid, particularly in the mornings, evenings and overnight, so results vary. A cooler does most on hot, dry afternoons and least on muggy days and warm, humid nights.
- It needs an open window or door nearby. In a closed room, humidity builds up and the cooling fades.
- The effect is most noticeable close up, as a cool breeze where you sit, rather than as a cooler room overall.
- Adding ice or very cold water gives a small, short-lived extra drop.
- It adds moisture, so it's a poor choice for a room that already gets condensation. Humidity and comfort explains why moisture in the air matters.
Looking after one
- Empty the tank and let it dry when you're not using the cooler, rather than leaving water standing for days.
- Clean the tank and clean or replace the pad as the manual describes, or the water can go stale and smell.
- Expect to top up the tank during a long, hot day.
- The fan is the main source of noise, so a cooler sounds much like a fan of a similar size.
Where one makes sense
A cooler can take the edge off the heat:
- on hot, dry days
- in a well-ventilated room, or a space with the doors open
- when you want a breeze close to where you sit, using little electricity
It isn't a good fit for humid weather, a bedroom with the windows shut, or cooling a whole room. For those, a portable air conditioner or a fixed system actually removes heat. Simple steps such as shading windows from the sun and ventilating when it's cooler outside can help too, as keeping cool without air conditioning describes.
Related guides
- Portable air conditionersA portable air conditioner is a self-contained unit on wheels that cools a room and sends the heat outside through a hose, usually out of a window. It needs no professional installation, but it is noisier and less effective than a fixed split system.
- Humidity and comfortHumidity changes how warm a room feels at the same temperature. Most people are comfortable with relative humidity of roughly 40–60%; above that, warm rooms feel close and sticky, and air conditioning helps by taking moisture out as it cools.
- Keeping cool without air conditioningKeep the sun off your windows during the day, open up when the air outside is cooler than inside, usually from late evening to early morning, and cut the heat produced indoors. Fans make you feel cooler, though they don't cool the room.