Measuring Humidity with Humidity Meters

Measurements taken with a hygrometer should always be made in a location that accurately reflects the actual indoor humidity. The ideal position is at a height of about 1.5 m, not directly against exterior walls, and at least one meter away from windows, doors, and radiators. Drafts or direct sunlight can significantly skew the readings. In rooms with high humidity levels - such as bathrooms, kitchens, or bedrooms - a central location is recommended so that the device can reliably detect typical humidity spikes. Even in basements or unheated rooms, hygrometer measurements should not be taken directly against cold surfaces, as condensation forms there and can cause the device to display unrealistically high readings. It is also important to allow the device to acclimate for a few minutes so that the sensor can adjust to the temperature and humidity. Devices from Gann, such as the Hydromette® BL Compact TF 3, are compact and portable, allowing measurements to be taken at various locations. Climate data loggers are available for professional use in building diagnostics.

A hygrometer measures relative humidity in percent - that is, the proportion of water vapor actually present relative to the maximum possible amount at the current temperature. In living spaces, levels between 40 and 60% are considered ideal. If the relative humidity falls below 35%, the air becomes too dry, which irritates the respiratory tract and mucous membranes. Conversely, levels above 65% increase the risk of mold, especially in poorly insulated areas. Household hygrometers typically measure in the range of about 20 to 90% RH. Professional devices provide reliable readings even beyond this range. Depending on the device, the measurement is taken either mechanically (e.g., using hair or synthetic fibers) or electronically via humidity sensors, which provide particularly fast and stable readings.

A hygrometer measures humidity and indicates how moist or dry the air in a room is. A hydrometer, on the other hand, is used in liquids to measure their density or specific gravity, for example in winemaking, brewing, or aquariums. A hydrometer works on the principle of buoyancy: the denser the liquid, the higher the device rises. A hygrometer, on the other hand, uses mechanical or electronic humidity sensors. Although the terms sound similar, the two instruments serve completely different purposes - air measurement versus liquid analysis.

Yes, hygrometers are extremely useful indoors because they help maintain a healthy indoor climate and detect moisture damage early on. They reliably indicate when the air is too humid - and thus promotes mold growth - or too dry - and irritates the respiratory tract, skin, and eyes. Especially in bedrooms, kitchens, bathrooms, basements, or new buildings, hygrometers provide important indications of when it’s necessary to ventilate thoroughly. This also helps prevent unnecessary heat loss. High-quality models - such as those combined with GANN measurement systems - also offer very high measurement accuracy for demanding applications. For example, the Hydromette® BL Compact TF-IR 2 enables a reliable assessment of conditions where temperatures fall below the dew point by combining surface temperature measurement via an infrared sensor with air humidity and air temperature measurements; it also allows for the detection of borderline situations on surfaces such as walls, ceilings, floors, and window and balcony door lintels.

The tolerance of a hygrometer depends on its design. Digital hygrometers typically have an accuracy of about ±2 to ±5% RH, while analog hair- or fiber-based meters often have an accuracy of ±5 to ±10% RH. It is important to note that accuracy is often temperature-dependent and that sensors can drift over time. Deviations can occur, particularly with lower-priced models, if the device has not been calibrated for a long time or is used under extreme conditions. It is therefore recommended to check the measurement accuracy regularly.

A hygrometer can be calibrated at home using the so-called salt method. To do this, place the device in an airtight bag along with a small dish of saturated salt solution. The solution creates a constant relative humidity of 75%, which serves as a reference after several hours. It is important to always allow the hygrometer to fully acclimate to room temperature before calibration. Alternatively, calibration can also be performed using special reference solutions or by comparing measurements with a precise reference instrument. For professional calibration, specialized calibration laboratories offer various humidity points, in contrast to the single-point calibration at 75% RH mentioned above.

Yes, digital hygrometers should also be calibrated regularly, as their sensors can lose accuracy due to aging, fine dust, temperature fluctuations, or prolonged storage. Although digital models are generally more stable and precise than analog hair-dryer hygrometers, it is recommended to check them once or twice a year. Calibration is particularly important for applications such as monitoring indoor air quality, preventing mold, or protecting sensitive materials. The salt method is the simplest procedure here as well. If the displayed value deviates significantly from the expected humidity level, or if high accuracy is required, the device should be checked sooner.