Description
High-precision measurements on swirl diffusers
Air volume flow is often measured on swirl diffusers, which create turbulent airflows that can easily lead to measurement errors. The testo 420 significantly reduces such errors thanks to its integrated flow straightener. This component neutralizes turbulence and converts irregular airflow into an almost laminar stream. Based on these uniform flow measurements, you can accurately calculate the air volume flow within a range of 80 to 3,500 m³/h.
Extremely lightweight and quick to assemble
The instrument features ergonomic handles and a display with a large tilt angle, weighing only 2.9 kg. This allows for precise and comfortable regular measurements in large spaces and at greater heights. The large start/stop button on the housing ensures easy recording of measured values.
The standard measuring hood dimensions are 610 x 610 mm. Other hood sizes are available as accessories. The optional tripod (up to 4 m height) greatly simplifies measurements at very high ceiling air outlets.
The device can be quickly assembled thanks to tension rods. The included trolley case ensures safe and convenient transport.
Create reports directly on site and send them via the mobile app
Take advantage of additional smart features by downloading the free mobile app. It allows you to connect your mobile device (smartphone or tablet) to the instrument via Bluetooth for use as a second display or for remote control — ideal for measurements on high ceilings using the tripod.
With the mobile app, you can start and stop measurements on HVAC systems, save data in .txt format, and create reports directly on site. Measurement results such as total air volume flow and air exchange rate can be inserted into custom templates. You can then send all data and reports via e-mail, saving time and increasing efficiency.
Additional instrument functions
The testo 420 comes with a display for reading measured values, which can be tilted or detached for convenience. It allows measurement of flow velocity, air volume flow, absolute pressure, temperature, and relative humidity. Automatic sensor zeroing ensures high accuracy in the low-pressure range.
All readings are easy to view on the large backlit display. Data can be stored for further analysis or used to generate reports on site using the mobile app. The plug & play function allows quick data transfer to a PC via USB without additional software.
The testo 420 can also be detached from the hood assembly and used for pressure, velocity, and volume flow measurements in ducts. This means you don’t need a separate instrument for these applications. Simply connect a Pitot tube and silicone hoses (available separately). Functions like time and point averaging and simple duct geometry input make the process even easier.
Delivery contents:
testo 420 measuring instrument including housing, 610 x 610 mm hood, 5 tension rods, USB cable, batteries, and trolley case.
Technical data
Temperature measurement
| Measuring range | -20 … +70 °C |
| Accuracy | ±0.5 °C (0 … +70 °C) ±0.8 °C (-20 … 0 °C) |
| Resolution | 0.1 °C |
| Response time | 45 s (t90) |
Humidity measurement
| Measuring range | 0 … 100 %RH |
| Accuracy | ±1.8 %RH + 3 % of measured value at +25 °C (5 … 80 %RH) |
| Resolution | 0.1 %RH |
Differential pressure measurement
| Measuring range | -120 … +120 Pa |
| Accuracy | ±2 % of measured value + 0.5 Pa at +22 °C, 1013 hPa |
| Resolution | 0.001 Pa |
| Response time | 1 s (t90) |
Absolute pressure measurement
| Measuring range | 700 … 1100 hPa |
| Accuracy | ±3 hPa |
| Resolution | 0.1 hPa |
| Response time | 1 s |
Air volume flow
| Measuring range | 40 … 4000 m³/h |
| Accuracy | ±3 % of measured value + 12 m³/h at +22 °C, 1013 hPa (85 … 3500 m³/h) |
| Resolution | 1 m³/h |
| Response time | 1 s (t90) |
General technical data
| EU Directives | 2004/108/EC |
| Warranty | 2 years |
| Battery type | Alkaline, AA |
| Battery life | 40 h |
| Display size | 3 x 5 in |
| Display | Matrix display with backlight |
| Interface | Micro-USB; Bluetooth® 4.0 wireless technology |
| Memory | 2 GB (integrated) |
| Storage temperature | -20 … +60 °C |
| Weight | 2900 g |
| Dimensions | 610 x 610 mm (standard hood) |
| Operating temperature | -5 … +50 °C |
Accessories
Stable, wheeled tripod with central adapter for safe work with high ceiling outlets.
| Measuring hood 360 x 360 mm | 0554 4200 |
| Measuring hood 305 x 1220 mm | 0554 4201 |
| Measuring hood 610 x 1220 mm | 0554 4202 |
| Telescopic tripod up to 4 m | 0554 4209 |
| Silicone hose, 5 m, max. load 700 hPa (mbar) | 0554 0440 |
| Differential pressure hose, 5 m, max. load 700 hPa (mbar) | 0554 0453 |
Pitot tubes (available separately)
| Pitot tube, 350 mm, stainless steel, operating temperature 0…+600 °C | 0635 2145 |
| Pitot tube, 500 mm, stainless steel, operating temperature 0…+600 °C | 0635 2045 |
| Pitot tube, 1000 mm, stainless steel, operating temperature 0…+600 °C | 0635 2345 |
Order no.: 0563 4200
Registered in the State System for Ensuring the Uniformity of Measurements of the Republic of Kazakhstan
since 27.12.2021, No. KZ.02.01.01360-2021
Valid until 27.12.2026
