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Thermohygrometer BZ21M
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  5. BZ21M thermohygrometer

Design thermohygrometer BZ21M

Perfect room climate control with all the values of analogue precision measurement technology

A healthy indoor climate has never been as valuable as today

Analogue precision measurement technology symbolises the tendency towards perfectionism and attention to detail in our fast-moving times. Characteristics that are also reflected by the BZ21M with its cross-needle design dial and classic appearance. From the indication of the room temperature and relative humidity to the display of absolute humidity and saturation humidity level: the timelessly beautiful hair hygrometer with thermohygrometer unites as many as four important room climate parameters on its informative dial, which are required for a healthy and comfortable indoor climate.

The thermohygrometer BZ21M monitors four important climate parameters:

  • Room temperature
  • Relative humidity
  • Absolute humidity
  • Saturation humidity

Being as precise as a Swiss clockwork and also following the high standards of classic watchmaking art on a visual level, the analogue measuring device convinces with a circular stainless steel housing (Ø 130 mm), high-quality mechanical measurement technology and a cross-needle scale design that is clearly legible even from afar. As there are no electronics integrated in the instrument, the BZ21M does not require any batteries or maintenance inspections.

Controlled heating and ventilation thanks to informative measured values

With its integrated suspension device, the visually appealing and attractive BZ21M can be used as a wall-mounted device to keep the focus on the essentials in living rooms, bedrooms, sauna areas, offices and training rooms: maintaining optimal room climate values to provide an asset for your health, well-being and performance. Likewise, the BZ21M makes critical temperature and humidity values in unheated garages, conservatories and storage rooms visible, which can lead to mould growth and expensive moisture damage without reheating or suitable ventilation.

Precise measurement data with high informative value

The thermohygrometer combines traditional measurement technology with an easy-to-read indication of the measured room climate values. Inside the device, the characteristic values are measured and the needles are moved by means of a bi-metal thermometer and a specially treated synthetic fibre that expands in humid conditions and contracts when it is dry. The resulting length variation is converted into a rotary motion using levers and axes and transferred to the needles in a way comparable to a clockwork.

Special scale design – displays the values and provides clarity

Thanks to its special dial design, all climate values are displayed in an easy-to-understand way and can be easily read even from a greater distance. Whereas other indoor climate measuring devices require a large number of needles and scales, the BZ21M scores with its unique cross-needle design dial.

Simple self-adjustment for permanently precise measurement results

If required, the display of the low-maintenance thermohygrometer can be readjusted by means of an easily accessible adjusting screw.

All four measured values are simultaneously displayed in an easy-to-understand way on the cross-needle design dial. This way, you create ideal conditions for always keeping an optimal overview of all important climate parameters.

Temperature measurement

Measuring range: 8 °C to 40 °C
Measurement accuracy: ± 2 °C

Humidity measurement

Relative humidity: 26 to 100 %
Absolute humidity: 2 to 50 g/m³

Saturation humidity: 2 to 50 g/m³
Measurement accuracy: ± 3 % RH

The high-quality analogue thermohygrometer BZ21M enables permanent control of as many as four important indoor climate parameters to ensure healthy and comfortable living quality.

Special equipment features of the BZ21M

BZ21M – dimensions
The true size of the compact BZ21M becomes apparent through its advantageous dimensions. With a convenient diameter of 13 cm, the dial is easy to read even from a distance. Despite having a depth of only 2.8 cm, the elegantly flat stainless steel housing simply stands out.
BZ21M – indication of the relative humidity
On the left-hand scale, the relative humidity is displayed in a measuring range from 26 to 100 %. Unwanted deviations from the desired target range become visible at one glance.
BZ21M – indication of the temperature and saturation humidity
The right-hand dual scale intelligently displays the room temperature (measuring range: 8 °C to 40 °C) and saturation humidity (measuring range: 2 to 50 g/m³) simultaneously.
BZ21M – indication of the absolute humidity
Displaying values ranging from 2 to 50 g/m³ in precise increments of 2 grams, the scale in the middle indicates how the measured climate parameters affect the absolute humidity of the room air.

Application examples from practical experience:

Thermohygrometer BZ21M – in the office
Too low humidity values in the office are not uncommon. With the visually appealing thermohygrometer BZ21M, you can keep an eye on the important parameters of a healthy working climate in order to counteract with controlled air humidification or dehumidification if necessary. Optimally regulated air humidity increases well-being at the workplace and reduces sick leave.
Thermohygrometer BZ21M – in the garage
There is no more stylish way to control the humidity level in the garage. The BZ21M is the visually perfect addition for vintage car garages, so you can keep an eye on the humidity level and prevent moisture-related corrosion. A permanently regulated humidity level protects against moisture damage and contributes to the value retention of your classic automobile.
Thermohygrometer BZ21M – in the bedroom
Excessive humidity in the bedroom is a common reason for mould growth. Prevent this health risk. The thermohygrometer BZ21M harmoniously blends into modern bedrooms and living rooms. Excessive humidity values requiring permanent dehumidification or the windows to be opened manually become visible at a glance.
Technical data by comparison

All climate measuring devices in direct comparison:

To find the climate measuring device which exactly meets your requirements, please consult the concise overview of all climate measuring devices from Trotec, which we're providing to you here so that you can compare them directly to each other.

Models which you do not wish to include in your comparison can be easily dismissed with only one click.

Technical data by comparison

A few practical benefits:

  • Four climate values on one dial: room temperature, relative humidity, absolute humidity and saturation humidity
  • Analogue precision measurement technology "Made in Germany".
  • Special cross-needle scale design
  • Easy to read, allowing a quick interpretation of the measured values
  • Adjustment option included


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Design thermohygrometer BZ21M

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84.95 £ 79.95 £ incl. VAT Show net price (VAT not included)


Technical data

Technical data
General information
  Article number 3.510.205.018
Air temperature [°C]
  Min. measuring range | Air temperature [°C] -10
  Max. measuring range | Air temperature [°C] 40
  Resolution [°C] 1
  Accuracy ± | Air temperature [°C] 2
  Accuracy [°C] 2
Relative humidity (%)
  Min. measuring range | Relative humidity [%] 20
  Max. measuring range | Relative humidity [%] 100
  Resolution | Relative humidity [%] 2
  Accuracy ± [% r.F.] 3
  Accuracy -10 °C - 40 °C - 20 % - 100 % [%] 3
Housing design
  Stainless steel
Ambient conditions
  Operation - min. temperature [°C] -20
  Operation - max. temperature [°C] 50
  Operation approx. - max. relative humidity (non-condensing) [%] 100
  Storage - min. temperature [°C] -20
  Storage - max. temperature [°C] 50
  Storage - max. relative humidity (non-condensing) [%] 100
  Length (packaging excluded) [mm] 130
  Height (packaging excluded) [mm] 28
  (packaging excluded) [kg] 0.185
Standard scope of delivery
Standard scope of delivery
  Operating manual
Ascertainable measured values and functions
Functions and features
  Measurement of air temperature and relative humidity
  Absolute humidity measurement
  Saturation humidity measurement

 standard equipment

 optionally available

 not available



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