Measuring air velocity: vane or thermal anemometer?
Air velocity can be measured with either a vane or a thermal anemometer, which differ in range and typical use. This guide shows which instrument fits where and how to determine airflow at ventilation outlets and in ducts correctly to DIN EN 12599.
View anemometersVane or thermal anemometer - which fits?
The sensor type defines both accuracy and application. A vane anemometer measures medium to high velocities with a rotating wheel and averages large areas well, while a thermal (hot-wire) anemometer uses a heated sensor to capture even the smallest air movement from around 0.1 m/s.
Large vane heads of 60 to 100 mm diameter suit supply and extract grilles because they average across the cross section. The slim sensor of the thermal anemometer instead fits through a bore into the duct and measures point by point at low velocities.
How do you determine airflow correctly?
Airflow equals the mean air velocity v times the free cross-sectional area A: Q = v x A. A velocity of 3 m/s in a duct of 0.2 m² therefore yields 0.6 m³/s, or roughly 2160 m³/h.
Because velocity is not uniform across the cross section, you measure at several points using a grid traverse and average them. DIN EN 12599 recommends 8 to 64 measuring points depending on duct size, evenly distributed over the area.
- Determine the free area A exactly; for grilles use the net area without the louvre share.
- Distribute measuring points evenly by grid traverse (log-Tchebycheff or centroid method).
- Keep at least six duct diameters distance from bends and dampers.
- Align the sensor against the flow and observe the airflow arrow.
- At the outlet use a flow hood to avoid edge turbulence.
What does the standard require at acceptance?
For the acceptance of air-handling systems DIN EN 12599 applies. It defines the measuring methods, the scope of testing and the permitted deviations; a tolerance of around 15 percent between target and actual airflow is common.
A calibrated measuring chain is essential: the anemometer should hold a valid calibration certificate and be checked regularly. Only then are the readings in the acceptance report reliable and legally sound.
Frequently asked questions
Which anemometer for ventilation outlets?
At supply and extract grilles a large vane anemometer works well because it averages over the area. With a flow hood you capture the outlet directly in m³/h.
How do I calculate airflow?
Airflow is mean velocity times free cross-sectional area: Q = v x A. At 3 m/s and 0.2 m² that gives 0.6 m³/s or about 2160 m³/h.
Why measure at several points?
Velocity is unevenly distributed across the cross section. DIN EN 12599 therefore requires a grid of 8 to 64 points whose average represents the real flow.
From what velocity is a thermal anemometer worth it?
Below roughly 1 m/s a vane starts too slowly. A thermal anemometer measures reliably from 0.1 m/s and suits ducts and room air currents.
Looking for the right anemometer?
We supply vane and thermal anemometers with airflow function and calibration certificate - suited to outlets and ducts to DIN EN 12599.
Calibrated
Instruments with a valid calibration certificate.
Wide range
Covering 0.1 to 40 m/s.
Direct m³/h
Airflow calculated automatically.
Standard compliant
Acceptance to DIN EN 12599 possible.