Which airflow instrument requires annual calibration, measures face velocity from 0 to 12,000 ft/min, and is a direct-reading, battery-operated device?

• A. Pitot Tube
• B. Vane Anemometer
• C. Hot-wire Anemometer
• D. Heated Wire Anemometer

Answer: (D)

A heated-wire anemometer is the type that fits this description. It uses a tiny heated element whose cooling by the airstream is related to air velocity; the instrument translates that cooling directly into a velocity reading on a display, and it runs on batteries for field use. This setup is capable of measuring a wide range of face velocities—up to about 12,000 ft/min—making it suitable for hood face velocity checks and similar tasks. Because the sensing element and electronics can drift with time, contamination, or environmental conditions, it requires annual calibration to keep readings accurate.

Pitot tubes measure pressure differences and need a separate manometer; they aren’t a direct-reading, battery-powered velocity meter. A vane anemometer provides direct readings but typically has different range limitations and mechanical wear concerns. Hot-wire and heated-wire instruments operate on similar thermal principles, but the heated-wire variant is the one widely specified for field, direct-reading measurements with the described calibration practice and velocity range.