Testo 405i Bluetooth Thermal Anemometer Smart Probe – Measuring the Air Inside and Out
The Testo 405i is a Bluetooth thermal anemometer smart probe designed for measuring air velocity, temperature and volume flow in ventilation ducts and indoor spaces that a vane anemometer can't reach — behind grilles, through service hatches or in cramped HVAC access points. It connects to a smartphone via the free Testo Smart App, which handles setup, live readings and reporting remotely.
Its hot wire sensor measures air velocity from 0 to 30 m/s with 0.01 m/s resolution, giving it useful accuracy at the low velocities where a vane probe starts to struggle. Being a probe rather than a full handheld device, it's also more practical to use in a duct: the probe stays in place while the phone acts as the display, rather than needing to read a small screen at the probe end from an awkward angle.
A 400mm extendable telescope gives access into ducts and tight spaces, and the Testo Smart App calculates volume flow automatically once duct dimensions and geometry are entered, alongside timed and multi-point mean calculations, trend analysis and data visualisation. Measurement logs can be exported as PDF or Excel files and emailed directly from site.
Beyond duct work, it can also be used to check indoor air velocity and detect draughts from non-airtight windows. When paired with the Testo 605i thermohygrometer (sold separately), it can also calculate cooling capacity and heating output for a fuller picture of HVAC system performance.
Temperature is measured via an NTC sensor across -20°C to +60°C, and the instrument runs on 3 x AAA batteries with a rated 50-hour battery life. A calibration protocol is included.
Key Features & Benefits
- Hot Wire Thermal Sensor: Measures air velocity from 0 to 30 m/s with 0.01 m/s resolution, accurate at low velocities where a vane anemometer struggles.
- 400mm Extendable Telescope: Reaches into ventilation ducts, behind grilles and through service hatches.
- Automatic Volume Flow Calculation: Enter duct dimensions and geometry once; the Testo Smart App calculates volume flow throughout the session.
- Remote Smartphone Operation: Read measurements from the phone while the probe stays in the duct.
- Timed & Multi-Point Mean Calculation: Averaged readings across a duct cross-section for commissioning documentation.
- Trend Analysis & Data Visualisation: Visual airflow data in the app to identify issues and communicate findings.
- PDF & Excel Reporting from Site: Email measurement logs directly from the app.
- Indoor Air Velocity & Window Airtightness Check: Detects draughts and checks indoor air velocity distribution.
- Pairs with Testo 605i: Combined cooling capacity and heating output assessment when used alongside the Testo 605i thermohygrometer (sold separately).
- Calibration Protocol Included: Ships ready for professional use on documented installations.
Ideal For
- Measuring air velocity in ventilation ducts.
- HVAC commissioning and diagnostics.
- Measuring volume flow in rectangular and circular ducts.
- Indoor air velocity checks and draught detection.
- Window airtightness investigation.
- Building services and ventilation engineers needing access to tight spaces.
Why Buy the Testo 405i?
The hot wire sensor reaches places a vane probe can't, and resolves down to 0.01 m/s, which matters for low-velocity diagnostic work where vane instruments start to lose accuracy. The 400mm telescope combined with phone-based readouts makes duct measurement genuinely easier — the probe stays in the duct while the display sits in hand rather than at the probe end. It's a useful addition alongside a vane instrument rather than a replacement for one: duct measurement and grille or outlet measurement are different jobs, and having the right tool for each makes a proper HVAC commissioning more accurate.
Order the Testo 405i Bluetooth Thermal Anemometer Smart Probe online today.
