First, you should decide if you want warm mist or cool mist. Then narrow it down further and choose a particular technology.
The difference between warm and cool is exactly what it sounds like, but thereís more to consider than just the temperature of the mist.
Warm mist humidifiers have a heating element. Heating the water aids evaporation, allowing the humidity to rise quickly, but it does take some time after switching on the unit for the water to heat through.
Producing heat uses a lot of electricity, so warm mist models will usually cost more to run.
If you have children, hot water may be something youíd rather avoid. (For obvious reasons!)
Some warm mist models only use heat, but many now combine multiple technologies so you get the best of both worlds. Any of the cool mist technologies can add heating to improve performance, and these hybrid models usually limit the heat used so the water doesnít get hot enough to risk burns.
If only heat is used, then the noise levels will be very low as there are no moving parts. For some people this is a big advantage. All you will hear is a light gurgling sound as the water bubbles.
If you donít heat the water then thereís no risk of burns and you use less electricity. That makes these methods a popular choice.
Imagine a wet sponge with a fan pointing at it, and thatís basically how they work. Except that the sponge is correctly known as a wick.
This is a very natural way to make water evaporate. The rate of evaporation is dependent on fan speed and how humid the air is to start with. Because of this, thereís little risk of over-humidification. The rate of evaporation slowing as humidity increases is a feature that other technologies use computer control to achieve, and complicated features like that donít come cheap.
The main disadvantage is the noise of the fan. Some people like to have a fan to mask background noise, which is particularly useful in cities. The sound can be relaxing, or it can be annoying. Itís a matter of personal preference.
The other disadvantage is that the wicks will need replacing on a regular basis, which adds to the cost.
Vibrating the water at an ultrasonic frequency to cause evaporation is the most modern technique. Itís very effective, possibly too effective at times. If you put them on too high a setting more moisture will be released than the air can hold and youíll find a puddle on the floor. This is rare though, and easily solved by using a lower setting.
You may see comments about white dust. Normally when water evaporates, mineral deposits are left behind. The vibrations can cause these deposits to be released. It depends on the water used how much deposit there would be. You can use purified water, or some models, like the Air-O-Swiss AOS 7144, have a demineralization cartridge.
They donít make much noise. With some you hear a buzz, and possibly a little water noise, but a good quality model will be very quiet.
This type is mainly mentioned for historical reasons as this technique is not used much these days. A spinning disk causes the mist. Usually these are quieter than a fan, but Ultrasonic is the technology of choice these days for those who want a low noise cool mist humidifier.
With every type of humidifier, they will only work well if they are maintained properly, with regular cleaning. Some models require less cleaning than others, as youíll read about on the Desirable Features page. Without exception though, a well maintained unit will be more efficient and economical than one that is not looked after.
Once youíve decided what type of humidifier to buy, itís time to make a wish list of desirable features, or jump straight to the reviews section and find the exact model that suits you best.