Testo 425 Thermal Anemometer - 0560 4251


0560 4251

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The functional testing of ventilation and air conditioning systems includes monitoring the flow speed in ventilation ducts. If the air flow velocity and volumetric flow are not set correctly, the room air quality may suffer. The testo 425 thermal anemometer measures the flow speed and automatically calculates the volumetric flow. 

In order to establish whether an air conditioning or ventilation system is functioning properly, among other things you need to check the flow speed or the volumetric flow in the ventilation duct. If the air flow velocity is too low, the room loads are not correctly discharged and optimum room air quality can no longer be guaranteed. 


  • 3 in 1 Measurements: temperature, air flow and volumetric flow calculation
  • Single & multi-point averaging
  • Extendable telescopic probe
  • Hold button to freeze readings

testo 425 thermal anemometer for quick, easy flow measurement 

The testo 425 thermal anemometer enables quick spot measurements in ventilation ducts. It records the flow speed, calculates the volumetric flow and also measures the temperature. With a measuring range of 0 to +20 m/s, the anemometer is particularly well suited to low air flow velocity. 

The thermal anemometer features a telescopic flow probe. The telescope can be extended to a length of up to 820 mm and has a probe head diameter of 7.5 mm. 

As well as flow speed, would you also like to detect the volumetric flow on your air conditioning or ventilation system? This is no problem for the testo 425 thermal anemometer. When you input the duct surface area, it automatically calculates the volumetric flow during the flow measurement. Single and multi-point averaging provides an indicator of the average volumetric flow, flow speed and temperature reading. 

You can read off the current readings and the min/max and calculated mean value at any time on the illuminated display. Using the Hold button, you can freeze the current reading in order to compare it with another value, for example. If you should ever forget to switch off the anemometer, the Auto-off function will take care of this for you. This conserves your batteries and ensures that your thermal anemometer is ready for use in the next measurement.


  • Testo 425 thermal anemometer
  • Protocol certificate
  • Battery


Technical Data

Storage Temperature -40 to +70 °C
Operating temperature -20 to +50 °C
Battery Type  9V block battery, 6F22
Battery life 20 h
Dimensions 182 x 64 x 40 mm
Product-/housing material ABS


Instrument Sensor

Sensor type Measuring range Accuracy Resolution
Velocity - Thermal  0 to +20 m/s ±(0.03 m/s +5% of m.v.) 0.01 m/s
Temperature - NTC --20 to +70 °C ±0.5 °C (0 to +60 °C)
±0.7 °C (remaining range)
0.1 °C


Buy with 100% confidence knowing your purchase is backed by the full Manufacturer's Warranty. Please register your product with provided warranty card.


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