Portable humidifier

A "portable" humidifier may range in size from a small tabletop appliance to a large floor-mounted unit. The water is usually supplied by manually filling the unit daily or on some periodic basis.

Evaporative humidifier [ edit ]
The most common portable humidifier, an "evaporative", "cool mist", or "wick humidifier", consists of just a few basic parts: a reservoir, wick and fan.
The wick is made of a porous material that absorbs water from the reservoir and provides a larger surface area for it to evaporate from. The fan is adjacent to the wick and blows air onto the wick to aid in the evaporation of the water. Evaporation from the wick is dependent on relative humidity . A room with low humidity will have a higher evaporation rate compared to a room with high humidity. Therefore, this type of humidifier is partially self-regulating; as the humidity of the room increases, the water vapor output naturally decreases.
These wicks become moldy if they are not dried out completely between fillings, and become saturated with mineral deposits over time. They regularly need rinsing or replacement; if this does not happen, air cannot pass through them, and the humidifier stops humidifying the area it is in and the water in the tank remains at the same level.
Natural humidifier [ edit ]
One type of evaporative humidifier makes use of just a reservoir and wick. Sometimes called a "natural humidifier", these are usually non-commercial devices that can be assembled at little or no cost. One version of a natural humidifier uses a stainless steel bowl, partially filled with water, covered by a towel. A waterproof weight is used to sink the towel in the center of the bowl. There is no need for a fan, because the water spreads through the towel by capillary action and the towel surface area is large enough to provide for rapid evaporation. The stainless steel bowl is much easier to clean than typical humidifier water tanks. This, in combination with daily or every other day replacement of the towel and periodic laundering, can control the problem with mold and bacteria.
Houseplants may also be used as natural humidifiers, since they evaporate water into the air through transpiration . Care must still be taken to prevent bacteria or mold in the soil from growing to excessive levels, or from dispersing into the air.
Vaporizer [ edit ]

Vaporizer (steam humidifier) (warm mist humidifier)
A vaporizer (steam humidifier, warm mist humidifier) heats or boils water, releasing steam and moisture into the air. A medicated inhalant can also be added to the steam vapor to help reduce coughs. Vaporizers may be more healthful than cool mist types of humidifiers because steam is less likely to convey mineral impurities or microorganisms from the standing water in the reservoir. [ 1 ] However, boiling water requires significantly more energy than other techniques. The heat source in poorly designed humidifiers can overheat, causing the product to melt, leak, and start fires.