Cool project. Will need to do similar soon at new place to deal with tech in a cupboard for heat.
900 is still quite high though - upper end of normal for indoor
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This is my attempt to fix groggy mornings by lowering my bedroom CO2 from 1700 ppm to ~900 ppm.
I designed a simple, 3D-printed fan duct that directs air under the door to improve air circulation.
A note on the design process: I used CadQuery, a Python library for creating parametric 3D models. I didn't know tools like this existed and highly recommend it if you can program; it turned out to be more convenient than manually iterating on prototypes in a GUI.
The project is open source and the post explains the full build. Happy to answer any questions.