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Ultrasonic, Steam or Evaporative Humidifier?

Edit: Zhejiang Oulun Electric Co.,Ltd    Date: 12-05-2013

Your choice of whether to buy a ultrasonic, steam or evaporative humidifier will depend on the specific application, your available budget and your acceptable level of maintenance.

All humidifiers will add water to an atmosphere by either boiling water to create steam, releasing very fine sprays of moisture that evaporate or by evaporating water from a moistened surface through which air is blown.

Spray / Ultrasonic (Warm or cool mist)
There are many cheap ultrasonic, mist type humidifiers on the market and these are often the most common type you'll find in the high street. An  ultrasonic humidifier contains a reservoir of water and an oscillating plate. The intense vibrations caused by the rapidly oscillating plate atomise the water into an airborne mist. A fan then blows this mist out of a vent and into the room.

As well as being economical to buy they also consume little energy when operating. However, the major disadvantage of using an ultrasonic humidifier is the dust that it introduces to a room. Any particulate matter that is present in the water will become airborne along with the water. When the water evaporates, the particulate matter will settle as dust in the room. This can aggravate symptoms in people with respiratory problems and therefore mitigate the beneficial effects of using the humidifier in the first place.

However, modern ultrasonic humidifiers (and all that are sold on this website) incorporate technology that prevents this dust from being released. High quality ultrasonic humidifiers use demineralisation cartridges that absorb the minerals from the water prior to it being turned into a mist. This is very effective as long as the cartridges are occasionally replaced inline with the manufacturer’s instructions. These types of modern ultrasonic humidifiers do cost more but the performance is head and shoulders above the cheap ultrasonic alternative.

Steam humidifiers provide very close control of humidity as the heat creating the steam can be rapidly increased or decreased in response to the room’s current humidity. However, to provide this control they need to be used in conjunction with a humidistat. This does the same job as a thermostat but instead of controlling a heating or cooling system to maintain a set temperature, it controls a humidifier or dehumidifier to maintain a room’s humidity.

Steam humidifiers provide very hygienic humidity control as the heating of the water kills all germs and the moisture released is sterile. A steam humidifier is the ideal choice for anyone with a respiratory illness, for raising the humidity in a nursery or for combating the symptoms of croup. They do need to be positioned out of reach when used in a nursery as the steam being release is obviously hot at the point of release.

This type of humidifier can be economical to buy in comparison with other humidifiers. Units that incorporate a humidistat can cost a bit more but have the advantage of not over-humidifying a room, saving energy and creating a more comfortable environment.

A disadvantage of using a steam humidifier is that they consume more energy than an ultrasonic or evaporative humidifier. A steam humidifier releasing up to 350g of water per hour may consume up to 325W per hour whereas an evaporative type of unit would only use between 10-20W.

The maintenance of a steam humidifier will involve occasionally removing the limescale that builds up inside the unit, similar to the scale that builds up in a kettle. This can be done relatively easily with a limescale removing powder. When not in use steam humidifiers should be emptied of water, cleaned and dried to prevent water stagnating inside the humidifier.

An evaporative humidifier introduces water into the air by allowing moisture to be simply evaporated. This consumes very little energy and is a hygienic way of humidifying as there are no aerosol sprays being released. Any particulate matter present in the water will remain in the humidifier after the water evaporates so there is no dust released into a room.

This type of system is also very quiet so can be used in a bedroom or similar quiet area.

There are two main types of evaporative humidifier. The more traditional type uses porous filters that are continually moisten and through which allow air is forced with a fan. As the air flows through the wet filter it picks up water and becomes optimally humidified.

The main disadvantage with this type of unit is that the filters need to be replaced regularly. The air in a home can be quite polluted with dust, skin, hair and other matter. These particles will be collected by the humidifier and remain on the filter as the air passes through. This has the advantage of cleaning the air but does mean the filters need replacing occasionally or they may begin to smell.

The other type of evaporative humidifier is an air washer. Instead of evaporative filters, an air washer incorporates many rotating discs that spin in a reservoir of water. A fan sucks air into the unit and forces it between the moist rotating discs, where it picks up water and becomes optimally humidified before being reintroduced into the room.

As the discs are made from toughened plastic, an air washer requires no replacement filters. The discs can simply be removed from the unit and cleaned. Some can even be placed in a dishwasher.

Cleaning will need to be carried out regularly to maintain hygienic operation but the frequency will depend on the quality of the room air.

Air washers have all the advantages of low running costs and air purification but with no ongoing commitment to buying spares. The disadvantage is that a quality air washer will cost more to buy than a filter-based evaporative humidifier but taking into account the savings on spares, the cost difference can soon be made up.