Hot Wire Thermal Anemometer – Testo 425

Model No: Testo 425Part No:0563 0425

The compact hot wire anemometer testo 425 with telescopic probe is ideal for simple, fast and precise determination of flow velocity and volume flow in ventilation ducts of air conditioning and ventilation systems. The connection to the testo Smart App enables configuration, display (also as second screen) and storage as well as documentation of the measurement directly in the App.

  1. Simple, fast and precise flow and temperature measurement plus volume flow calculation in the ventilation duct
  2. More flexibility for duct measurements with the cable-connected telescopic probe (maximum length 820 mm)
  3. Fast in-app (duct) configuration, graph history, second screen and measurement data memory in the testo Smart App
  4. Timed and point mean value calculation


Optimally adjusted air conditioning and ventilation systems are a decisive factor for modern buildings. Accordingly, it is important to use the appropriate measurement technology to ensure that the flow, temperature and volume flow in the ventilation duct are correct. The testo 425 thermal anemometer is your fast, easy and precise companion. The cable-connected telescopic probe can be extended up to 820 mm, making it easier to work overhead or in large diameter ducts. All relevant calculations, such as volume flow or time and point averages, are performed automatically by the particularly robust and compact measuring instrument. Incidentally: Configuration of the measuring instrument, display and storage of measured values as well as documentation are all particularly convenient with the testo Smart App. This also turns your smartphone into a second display.

Scope of delivery

  • testo 425 – Thermal hot wire anemometer with App connection and fixed telescope (max. 820 mm)
  • Transport bag
  • Calibration protocol
  • 3 x AA batteries

Technical Data

Temperature – NTC
Measuring range -20 to +70°C
Accuracy ±0.5°C (0 to +60°C), ±0.7°C (Remaining Range)
Resolution 0.1 °C
Velocity – Thermal Probe
Measuring range 0 to +20 m/s
Accuracy ±(0.03 m/s + 5 % of mv)
Resolution 0.01 m/s
General technical data
Operating temperature -20 to +50 °C
Storage temperature -40 to +70 °C
Battery type 9V block batter



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