Ventilation air flow check with cheap anemometer

We have a ventilation system in our house. From time to time we want to make sure that it still supplies us with the correct amount of fresh air.
A professional air flow measurement system is quite expensive. But by using a cheap anemometer you can achieve the same result.

With the funnel and the adapter all the air from an outlet flows through the anemometer. It shows the wind speed v in m/s. To calculate the air flow in m³/h we need the area A=pi*(d/2)².

My anemometer has d=2.5 cm. A=4.9E-4 m².
Air flow = v A 3600 = v * 1.8 [m³/h].

E.g.: v=5 m/s => Air flow=9 m³/h

The funnel was designed to fit over the outlet.
The anemometer fits in the adapter-box, which connects the the funnel.

My slicer didn't generate good support structures. So I added some myself in the design. Hence the adapter box comes in two versions: with and without support.
If you print with my support structures then you can use a screwdriver to remove them.

Since your anemometer and outlet might have another size, the OpenSCAD source is also there. So you can adjust it to your needs.