Swirl flowmeters can be utilized for highly accurate measurement of the flow of gases, liquids and steam over a wide range of temperatures in almost any application ...

Pinwheels are pretty optimized from a design standpoint, and are so cheap and easy to build that putting a pinwheel to work as an HVAC duct flow meter seems ... experiments in air duct flow ...

Air flow sensors are inserted into a duct or pipe through an access hole to measure air velocity. In other instances a capture hood is used to measure volumetric flow from a grill or exhaust diffuser.

Measuring air flow in an HVAC duct can be a tricky business. Paddle wheel and turbine flow meters introduce not only resistance but maintenance issue due to accumulated dust and debris.