Quick answer: The testo 410i measures air velocity, but the appropriate measurement geometry differs: the 405i is a hot-wire duct probe, whereas the 410i uses a small vane suited to accessible flow areas and outlets.
What makes the testo 410i different
The testo 410i uses a 30-mm vane and reads air velocity and temperature; the companion app derives volume flow using entered geometry. It is useful at vents and appropriate outlet/duct situations, but differs from the 405i hot-wire probe.
Prepare and carry out the measurement
- Document the measurement objective: local velocity at a point or volumetric airflow across an opening.
- Select a measurement location with reasonably developed flow and orient the sensor as its manual describes.
- Record multiple points or a timed average rather than relying on a single maximum; identify the actual effective cross-sectional area.
- Calculate volume flow from representative mean velocity and area, then compare at the same fan/damper condition.
Model-specific use and interpretation
Orient the vane with the local flow, avoid obstructing the outlet, use multipoint/timed averaging in the app and verify the entered outlet area. Document whether the reading was free-stream or in a grille flow profile. For broader guidance on vane alignment, averaging and outlet geometry, see the vane anemometer measurement guide.
Velocity in m/s multiplied by area in m² gives m³/s. For CFM, use the properly converted flow; the result is not the same as useful outdoor ventilation unless outdoor-air fraction is separately known.
A face reading multiplied by nominal grille dimensions can exaggerate or understate delivered flow when the free area or velocity profile is unknown.
Worked example (hypothetical)
Hypothetical mean velocity 2.0 m/s through a correctly established 0.15 m² opening gives 0.30 m³/s, or about 636 CFM. A central peak of 3.0 m/s would produce a misleading estimate if used for the whole area.
Why the 410i is not a replacement for every duct probe
The 410i has a compact vane suited to accessible ventilation outlets and some duct situations. The vane requires a suitable velocity direction and sufficient measurement space; a small grille can produce nonuniform jets that make centre readings unreliable. Use the app’s timed/multipoint averaging and document effective area rather than multiplying by an arbitrary grille face size. For a low-speed or inaccessible duct traverse, a different probe type may be better.
Interpretation: If a grille has a nominal 0.25 m² face but only 0.18 m² effective area, using the larger area exaggerates calculated flow by about 39% at the same mean velocity. For more detail on single-reading limitations and duct traverses, see this guide.
Limits and safety
Follow the exact instrument manual and the equipment manufacturer’s acceptance criteria. The example is not field evidence, a legal limit or a commissioning target. Work on energized electrical equipment, combustion systems, charged refrigerant circuits or hot surfaces requires qualified personnel and the site’s approved protective procedures.