Humidifier guide


Air is the basis of our lifes. Every day, we breathe in and out 20’000 times on average, which corresponds to around 12’000 liters of air – and we need that daily. The quality of this air has a direct effect on our well-being and productivity.

An optimal air humidity plays an important role. This is measured with a hygrometer (e.g. Selina by Stadler Form). For homes and offices, a relative humidity of 40 – 60% is perceived as pleasant and recommended. Especially for the bedroom these values enhance the nightly rest noticeably. Air humidifiers improve indoor air quality by maintaining optimal humidity of the air.

Medical professionals recommend a relative humidity of between 40 – 60%. If the air is dry, we suffer from burning eyes, dry skin, irritated mucous membranes, we do not sleep as well and are more susceptible to catching a cold or the flu.

Building materials and interior furnishings made of wood or fabric (e.g. curtains or carpets) absorb lots of moisture. If the air in a room is dry, cracks can form (wood) or an electrostatic charge (fabric) can develop. Musical instruments made of wood can go out of tune if the wood dries out.

Cold air contains less moisture than warmer air. For this reason, humidity in interior rooms often drops below 30% in winter. The greater the difference between outside and inside temperature in winter, the dryer the air in the room is. It is easiest if you measure relative humidity with a hygrometer. Position the hygrometer in the centre of the room, away from windows and doors, and simply read the humidity on the display (e.g. Selina by Stadler Form). You need a humidifier if the humidity is below 40 %. If the humidity is above 60 %, using a dehumidifier is recommended so as to prevent mould formation.

To open the windows does not help to increase the air humidity in the room in the cold half of the year. Regular, brief intermittent and cross-airing is very important for the air we breathe to be healthy (3-5 x a day in winter for a maximum of five minutes). However, airing too often and for too long with cold outside air makes the air in the room even dryer. This also applies to tilted windows. This is because outside air contains less moisture and becomes even dryer as it is warmed up by the heat. See also Why does the air get dry?

House plants, showering, cooking and wet clothes can indeed raise the humidity slightly for a short time, but they are not able to take the humidity to an optimum level of 40 to 60% over a longer period of time and where the air in a room is very dry. Wet towels or bowls filled with water on radiators also only help to achieve a slightly higher humidity in the short term and frequently become a source of germs if they are not washed regularly.

Flu viruses, bacteria and germs survive for longer in dry air and float at eye level for a longer period of time. This is how dry air promotes the transmission of flu viruses and bacteria. An optimum humidity of between 40 and 60 % ensures that viruses and bacteria bind to the water droplets in the air and drop to the floor as a result. A healthy relative humidity does not only help to optimally moisten the mucous membranes and therefore strengthen their defences against attack, it also helps to reduce the susceptibility to infection.

An optimum room humidity of between 40 and 60% ensures that the air is less contaminated by pollen, dust and other particles. These contaminant particles attach themselves to the water droplets in the air, become heavy, and drop to the floor. When on the floor, they are less of a burden to your airways than they are when floating at eye level. Allergy sufferers can relax and take a deep breath.

Passive houses are a great invention and help to create energy-efficient living. However, if the controlled ventilation system does not have a mechanism for regulating the humidity, very dry air in the room is the result. Continuous air exchange is the reason: Cold and dry outside air is heated and brought inside. The moisture produced by people, animals, furniture, plants, cooking, showering etc. is quickly taken outside as a result of the continuous air exchange. Extremely dry air in the room is usually the result. Use a hygrometer to ascertain the current humidity of the air. Position the hygrometer in the room (not in the vicinity of windows, doors or ventilation slots) and read the relative humidity off of the display (e.g. Selina by Stadler Form). You need a humidifier if the humidity is below 40%. 

Controlled ventilation systems act like open windows. That is why, for ventilated rooms, we recommend more powerful humidifiers and room size calculations that are double those for non-ventilated rooms (e.g. Oskar for non-ventilated rooms up to 50 m² and for ventilated rooms up to 25 m²).

Before you purchase a humidifier or dehumidifier, it is important to measure the current relative humidity beforehand. It is easiest to do this with a digital hygrometer (e.g. Selina by Stadler Form). Set Selina up in the centre of the room at hip or eye level. Make sure that you do not position the hygrometer in the vicinity of windows, doors or ventilation grilles. After a couple of minutes, the sensor will have adjusted to the room temperature and you can read off the relative humidity. Medical professionals recommend a humidity of between 40 – 60 %. Below 40 % the air in the room is too dry and above 60 % it is too moist. Air in the room that is too dry can be raised to an optimum level with a humidifier. Air in the room that is too moist can be lowered to an optimum level with a dehumidifier.

You can find out which product is the right one for your needs using our product advisor.

Dry air primarily occurs in winter, when heating is used a great deal and indoor humidity often falls below 30 %. Opening the window doesn‘t help; quite the opposite, the air in the room becomes even dryer. Outdoor air at a temperature of around 0 °C can only hold 4 grams of water per cubic meter. However, at an indoor temperature of around 20 °C, the air can hold 20 grams per cubic meter. Even if the relative humidity outside is 69 %, this corresponds to a relative humidity of just 18 % inside. By opening the window, the amount of water in the air remains the same, but the relative air humidity falls as the temperature rises. This moisture deficit can only be overcome with the aid of an air humidifier. The ideal relative air humidity recommended by doctors is 40 – 60 %.

  • Your nose, eyes and skin will no longer feel dry: You will feel more comfortable at home.
  • The risk of catching the flu is reduced: The influenza virus survives for less time in rooms with optimum humidity. The risk of infection is considerably reduced at higher humidities. There will be less stress on your mucous membranes and less chance of you falling ill.
  • You and your family will sleep better: Dry air is not good for you. Enjoy  better and more restful sleep when the humidity is optimal.
  • You will be able to concentrate better: You will feel less listless and tired  and your ability to concentrate improves.
  • Dust and pollen exposure will be reduced: Even Allergy sufferers can take a  deep breath, moist air binds dust particles and pollen.
  • Furniture, wooden floors and paintings will be protected: Cracks and  deformation will be avoided.
  • Instruments will not de-tune: You do not need to frequently retune pianos,  guitars and violins.

It is important to measure the relative humidity correctly. A digital hygrometer, such as Selina by Stadler Form, can take care of this task. Selina is ready for use right out of the box. Put the hygrometer on a raised surface in the centre of the room away from windows and doors. The sensor needs the first couple of minutes to adjust to the room temperature. Afterwards, the relative humidity is displayed. Medical professionals recommend a relative humidity of between 40 – 60 %.

Dry air in the room manifests itself through irritated mucous membranes, dry skin, cracked lips, burning eyes, electro-statically charged hair, headaches, poorer quality of sleep, cracks in parquet flooring and wooden furniture, musical instruments that go out of tune, etc.

Moist air can be the reason for a bad smell in the room, dark marks on walls and window frames as well as water droplets on walls and windows. Check your walls and furniture (the wall behind a cupboard especially) for traces of mould. It is essential that you contact a specialist to have the mould removed professionally. Black mould in particular has adverse health effects.

Relative humidity

Describes the relationship between absolute and maximum humidity in percentage terms. The water quantity actually present in the air is referred to as absolute humidity. Maximum humidity is understood as the maximum possible water quantity in the air at the current temperature. The air can absorb more or less water depending on the temperature. The colder the air, the less water it can absorb – the warmer the air, the more water it can absorb.
50 % relative humidity therefore means that half of the possible water quantity at the current temperature is actually present. 100 % means the air is completely saturated with water which corresponds, in absolute terms, to maximum humidity.

Humidifier performance

Shows how many grams of water the humidifier can discharge into the air in the room in one hour.

Room size

Depending on the system and model, a range of room sizes can be humidified. Please see the manufacturer‘s information. For larger rooms it is necessary to use several devices to achieve the desired humidity level. The area of the room is used to calculate the room size, as well as the height of the room.


The hygrostat can be used to set the desired relative air humidity. The device switches off automatically when the desired humidity is reached. If the humidity falls, the humidifier switches on again.

Germs and bacteria

Whenever water is left standing, germs and bacteria can develop. This problem is avoided with vaporizers, because the water in the device is boiled, but for all other systems we recommend the use of the Ionic Silver Cube™ to inhibit growth.

White Dust

«White dust» occurs with ultrasonic nebulizers because these emit limescale particles into the air. The problem can be reduced by using an anticalc cartridge.

Water Hardness

The composition of tap water differs greatly on a regional basis. If you have very hard water (more than 21 German degrees), we recommend the use of an evaporator or air washer.

Download humidifier guide