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 like a great idea. Great in theory ...

Description: Rheotherm flow sensing probes for duct gases are easy to install and provide long-term service with little or no maintenance. The output can be in mass, standard volume or velocity units.

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.