Ventilation aid BelAir hygrometer

When does it make sense to ventilate a room to achieve the right humidity level?

The new BEL-AIR can answer this question by simultaneously measuring the temperature and humidity values indoors and outdoors.

This is a question that is often asked today, particularly because of the problem of mold, and the answer is not always easy even for a specialist or experienced weather observer. With the BEL-AIR digital combination measuring device, this question is continuously answered via the display.

Particularly in historic church interiors, the reduced heating activity results in over-humidification of the room air and thus moisture precipitation on cold surfaces, e.g. walls or organ parts. Together with a layer of dust, these are an ideal breeding ground for the mold spores that are always present in the room air. The result is a visible coating of mold. The formation of mold can be counteracted by avoiding this excess humidity in the room by airing the room in good time when the outside conditions are appropriate. The BEL-AIR is a great and inexpensive help for this, so that you can open or close the windows at the right time. Due to the often inadequate ventilation possibilities in historic churches, the installation of electric exhaust fans should also be considered. Even in large rooms, normal bathroom ventilators provide useful exhaust air. Installed in any existing ceiling holes, excessively humid room air can be extracted into the attic area at certain times.

The combination device consists of a convenient indoor thermohygrometer with a large digital display for the indoor values and a receiver for the wireless outdoor sensor with a range of up to 100 m. The digital display also provides you with the appropriate information for your ventilation behavior.

Based on the indoor and outdoor values, the device calculates the resulting change in humidity in the interior when ventilation is planned and gives you the following information using 5 display fields: Center: "No change" No change necessary Left RED: "More wet" When ventilating, the room becomes more humid Right GREEN: "More dry" When ventilating, the room becomes drier Outside left: Ventilate without fail - open window (only displayed if necessary) Outside right: Do NOT ventilate - keep window closed (only displayed if necessary) The display also has an optical pointer that indicates the current humidity level.

Dimensions: Indoor unit with display 160 x 95 x 20 mm Outdoor sensor 100 x 40 x 25

Batteries: 2 AAA 1.5 V batteries not included!

Indoor and outdoor unit always supplied together!

Please note that comprehensive advice on the special use of these devices for end users is not included in the device price. Specialists on site, such as climate consultants, organ builders, organ experts, will charge for their consulting services on a time basis.

When installing the outdoor sensor, make sure that it is mounted on the north side of the building and in a position without direct sunlight to ensure correct measurement.

If you are looking for a general overview of various hand-held meters, please click here. Please click on the following link in our digital catalog Thermo-Hygrometer and various hand-held measuring devices. hand-held meters.

We also carry liquids for the treatment of mold on walls and objects. If you are interested, please click on Fungo products for further information.


Observation from practice

The photo shows the display on a midsummer's day in the morning. Based on gut feeling, one would say that the still cooler outside air should be let into the room.

However, the measuring device tells you to keep the windows closed, as the relative humidity outside is very high and opening the windows would lower the temperature in the room, but the relative humidity in the room would continue to rise. Over-humidification of the room with subsequent storage of moisture in the walls over time would be the basis for mold growth.

Click on the photo to enlarge it.

Product variants
Part number
Net price
Gross price
BEL-AIR ventilation thermo/hygrometer digital indoor and outdoor without batteries
37,50 €
44,63 €
BEL-AIR Lüftungs- Thermo/Hygrometer digital innen und außen ohne Batterien - Einzelpreis bei Mengenabnahme ab 3 Stück -
32,50 €
38,68 €