daily basis. Bottom fill Bottom filled humidifiers has removable water tank, often attached with a replaceable demineralization filter. Both the cap and the filter are often universal, which means that they can be switched between many tank cap humidifiers. Tank cap-based humidifiers are more inconvenient to fill than top fill tanks, because the demineralization filter has to be unscrewed and screwed back on a daily basis. Also, water drops from the tank attachment may get in contact with the hygrometer, which will make it harder to operate properly if they are not operated with caution. Features Cleanable Ultrasonic wave nebulizers trap the mineral deposits over time, even if filters are used, and require cleaning with vinegar or citric acid to control buildup. It is easy to remove the buildup from the nebulizer in humidifiers with removable base parts. Other models must be screwed. Some models require monthly maintenance, while other models may run for years unmaintained. Activated charcoal filter Some humidifiers have an activated charcoal filter to reduce contaminants. Demineralization filter Humidity with mineral deposits build up on furniture, and static objects like computer monitors, TVs, etc. Most models with heating elements come with replacement demineralization filters (cartridges, or plastic foam, for the tank, and fabric near the heater in the reservoir) to reduce the amount of minerals entering the system. The cost of these filters is about $10-15 per cartridge or 10-pack for plastic foam, or fabric filters. Cartridges may last for 6 months, and plastic foam/fabric filters may last one month, if the humidifier is frequently used. Cartridges can be used for most humidifiers, but some models have a proprietary format. Some humidifiers (for example, some cold mist humidifiers) don't come with any filters at all. Clogged filters should be replaced when they cannot deliver water, which is indicated with a "no water" icon/alert signal in modern humidifiers. A manual way to figure out if a filter is clogged is to shake it, if the content of it (even if wet) doesn't move around, then it's unlikely that sufficient water will pass through. Heating element Steam humidifiers, or warm mist humidifiers, are equipped with a heating element. A medicated inhalant can also be added to the steam vapor to help reduce cough. Vaporizers may be healthier than cool mist types of humidifiers because steam is less likely to convey mineral impurities or microorganisms from the standing water in