When is a humidifier useful? Signs and target value

In the morning your nose is dry, your throat feels scratchy, and the hygrometer in the bedroom shows less than 40 percent. Many people know this as soon as the heating comes back on in autumn. But a dry throat alone does not tell you how dry the air in the room really is. Whether a humidifier is useful depends above all on how long the air stays too dry. In this guide we show you how to recognise overly dry indoor air, which target value is right and how to set up and care for an air humidifier such as our Beurer LB 300 Plus.

How to recognise overly dry indoor air

You can recognise overly dry indoor air through your body and through a measured value. People often feel unwell when the relative humidity in a room stays well below 30 percent for a longer period.^[1] Values below 30 percent dry out the mucous membranes.^[2] Even below 35 percent, dry air can irritate the airways.^[3]

Your eyes also react to the indoor climate. Dry air and draughts, air conditioning and fan heaters are among the possible causes of dry eyes.^[4] So if you sit in front of a screen in the evening and your eyes start to burn, it is worth checking the humidity in the room as well.

How reliable is the feeling alone? A scratchy throat can have many causes. That is why we recommend measuring the humidity before you decide. A thermo-hygrometer shows you the value at any time. Which devices measure accurately is covered in our guide to hygrometers.

When indoor air becomes too dry in winter

Indoor air becomes too dry in winter when the heating is on and hardly any moisture is added. In winter, heating makes the air indoors dry. A relative humidity between 40 and 60 percent is ideal.^[3][1]

Especially when the radiators are on, closed rooms usually fall short of the recommended range of 40 to 60 percent. This is particularly noticeable in the bedroom, where you spend many hours at a stretch and the door often stays closed. A single dry day says little. But if the value stays below 40 percent for days and weeks, it is worth taking a closer look at possible solutions.

Airing or humidifying: what helps against dry air

Regular airing helps against dry air, and if that is not enough, a humidifier does. To raise the humidity a little, it can help to air the room thoroughly at regular intervals. If the air stays dry for a longer period, however, we recommend using an air humidifier, such as one of our Beurer air humidifiers.

Both approaches complement each other. Regular airing exchanges the air and helps keep it from becoming too dry. Humidifiers can help keep the air moist.^[3] For dry eyes, too, humidifying the indoor air is one of the simple changes you can make in everyday life.^[4]

But when is airing enough, and when is a device the better choice? The overview below helps you interpret your reading.

If the humidity in your home tends to rise too high, for example in the cellar or in a bathroom without a window, our dehumidifiers are the right devices. They draw excess moisture out of the air and so lower the relative humidity in the room.

How the Beurer LB 300 Plus humidifies the air

The Beurer LB 300 Plus humidifies the air using natural cold evaporation — powerful, and pleasantly quiet on low settings. The evaporation filter soaks up water like a sponge. The fan draws the dry room air into the unit and passes it over the moist filter, where the water evaporates from its surface. The fan then distributes the humidified air evenly throughout the room thanks to its 360° design.

The LB 300 Plus is suitable for rooms of up to 45 m² and achieves a humidification output of up to 300 ml/h. Its water tank holds 3.0 litres. For the bedroom, it has a night mode with quiet operation and no disturbing lighting, plus a timer function from 1 to 9 hours. A water level sensor monitors the tank, and when the tank is empty the device switches itself off with the safety switch-off. We give a 3-year guarantee on the LB 300 Plus.

The LB 300 Plus has also performed well in tests. At Stiftung Warentest it is “Testsieger”, GUT (1.9), in a test of 8 humidifiers, test issue 10/2025.^[1] In ETM TESTMAGAZIN, “6 Luftbefeuchter im Test 2026” (26.02.2026), it received the rating Sehr gut (93.9 %) on the ETM TESTMAGAZIN percentage scale, with 6 devices in the test field.^[5] The F.A.Z. Kaufkompass, “Der beste Luftbefeuchter” (05.08.2026), lists it among 59 devices tested with the award “Auch gut”.^[6]

Which unit suits you best depends mainly on the size of your room. The LB 300 Plus is suitable for rooms up to 45 m², so it also works well in large living rooms. For smaller rooms, we offer other humidifiers in our range: the Beurer LB 200 also uses cold evaporation and is suitable for rooms up to 30 m². The Beurer LB 37 humidifies rooms up to 20 m², such as a child's bedroom or a small home office. For rooms up to 50 m², there is the Beurer LB 55.

Besides cold evaporation, there are other types, such as ultrasonic humidifiers and steam humidifiers, which we compare in our guide to humidifier types.

Setting the target value of 40 to 60 percent

You set the target value on the LB 300 Plus using three humidification levels, which allow a constant relative humidity of 40, 50 or 60 percent. That way, every level keeps you within the recommended range. In the intelligent automatic mode, the LB 300 Plus measures the current humidity and adjusts its output to the desired humidity level.

Why is a fixed target value so important? Humidity above 65 percent can encourage mould growth.^[3] A fixed target value helps you stay safely below this limit. On the LB 300 Plus, the automatic mode takes care of this for you. You do not need to readjust anything.

To help you keep an eye on the value, the LB 300 Plus displays the humidity on a digital display. A coloured LED ring additionally shows you at a glance how humid the room air currently is. In general, we recommend monitoring the humidity with a hygrometer so that you can use a humidifier in a targeted way and avoid humidity that is too high.

For the bedroom, the night mode with the timer is worthwhile, so that the device only runs as long as you need it. Which devices are particularly quiet is covered in our guide to quiet humidifiers for bedrooms and children's rooms.

Humidifying hygienically: cleaning and maintenance

Humidifying hygienically means emptying, drying and descaling the device regularly. This matters so that your humidifier stays hygienic in the long term. On the LB 300 Plus, a few features make care easy for you.

If the LB 300 Plus is not in use, mould and bacteria can form in the filter. You should therefore always empty the remaining water from the tank and dry all parts. The filter drying function dries the filter after use to reduce bacterial growth. This is how to start it on the LB 300 Plus:

1. Empty the remaining water from the tank and dry any moisture under the filter holder by hand.
2. Press and hold the fan speed button for 5 seconds.
3. The LB 300 Plus now dries the filter for 3 hours at the highest setting.
4. Then check whether the filter is completely dry and start the function again if necessary.

For regular care, we recommend descaling the filter and water tank of the LB 300 Plus every week. A citric acid solution of 6 g of pure citric acid powder per 1 litre of water is suitable for descaling; leave the parts to soak in it for one hour. Then rinse everything thoroughly under running water without squeezing the filter. From time to time you can also clean the water tank, filter holder and water level sensor in the dishwasher, at a maximum of 45 °C.

You should replace the filter after 6 months at the latest. After 1440 operating hours, the filter change indicator on the LB 300 Plus reminds you. Before you store the device, you should empty and clean it, because no water should be left in the tank while the device is not in use.

Setting up and using the humidifier safely

Place the LB 300 Plus on a level, horizontal and stable surface, with 30 cm of clearance on all sides. Read the instructions for use before using it for the first time. When using the LB 300 Plus:

• Let the filter absorb water for 30 minutes before switching the device on for the first time, so that the humidification output is optimal.
• Fill the tank up to the “Max.” mark with cold tap water or distilled water; the water temperature should not exceed 40 °C.
• You should not operate the device in rooms with high humidity or large temperature fluctuations, such as the bathroom or kitchen.
• Do not add fragrances or chemical substances to the water.
• If the area around the device becomes damp, reduce the humidification output. Carpets, curtains and tablecloths should not get damp.
• Always supervise children when they are near the device.
• The remaining water is not drinking water. Pour it down the drain and do not use it for animals or plants either.

If the air in your home stays too dry for weeks, an air humidifier with a fixed target value is the simplest solution. Take a look at our Beurer air humidifiers and find the one that suits your room.