testo 425 - Compact Thermal Anemometer

Order-Nr.  0560 4251

  • Temperature and flow measurement as well as volumetric flow calculation

  • Permanently attached extendible telescopic probe – maximum length 820 mm, diameter 7.5 mm

  • With single and multi-point averaging

  • Hold function, display of min/max value, Auto-off function

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.

Delivery time: 3 – 5 working days

Shipping costs

£ 359.00
incl. VAT  £ 430.80

Product Description


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.

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.

Equip yourself with accessories for the anemometer

To make sure that you are well-prepared for any circumstances, we recommend that when purchasing the anemometer, you also order our practical accessories: as an added option we offer a handy pocket, a transport case and also the TopSafe protective cover (to protect the anemometer from water, dirt and impacts).


Delivery Scope

testo 425 - Compact Thermal Anemometer with fixed velocity probe, temperature measurement and telescope (max. 820 mm), battery and calibration protocol

General technical data


285 g


182 x 64 x 40 mm

Operating temperature

-20 to +50 °C

Product-/housing material


Battery type

9V block battery, 6F22

Battery life

20 h

Storage temperature

-40 to +70 °C

Temperature - NTC

Measuring range

-20 to +70 °C


±0.5 °C (0 to +60 °C)

±0.7 °C (Remaining Range)


0.1 °C

Velocity -Thermal anemometer

Measuring range

0 to +20 m/s


±(0.03 m/s + 5 % of mv)


0.01 m/s


9V rech. battery for instrument

Order Number: 0515 0025

£ 15.00
incl. VAT  £ 18.00
£ 26.00
incl. VAT  £ 31.20
£ 29.00
incl. VAT  £ 34.80


Order Number: 0516 1201

£ 39.00
incl. VAT  £ 46.80

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