Show HN: I built an under-the-door fan duct to lower bedroom CO2

Hi HN,

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.

Show HN: I built an under-the-door fan duct to lower bedroom CO2
lepekhin.com

Generating negative pressure in a room isn't great for fresh air. You'll be sucking air through any opening- wall outlets, floor registers, ceiling light fixtures, gaps in baseboard trim, etc.

Might be simpler to augment your fresh air intake with a fan.

Or just open a window, you'll also sleep better

Given the effort involved (unusually-shaped 3D printed duct and housing for the whole gizmo), ISTM it would make a lot more sense to fit the duct to the trickle vent and operate it in positive pressure mode. This would have lots of advantages:

- With positive pressure, the intake air doesn't pick up contaminants from the wall cavities and other nooks and crannies within the building envelope.

- A fresh air supply fan can be fitted with a high-quality filter (HEPA or near-HEPA) to supply air with approximately zero PM2.5. (This is a very, very effecive way to get indoor air that is cleaner than the outdoor air without substantial power consumption.)

- You can open the door without moving the fan! You can leave it on with the door open! And it may improve the air quality in the rest of the living space more than the under-the-door scheme.

In a very cold climate, it might make more sense to put something like this in a different room so that the unconditioned supply air could be mixed with conditioned indoor air farther from where anyone is trying to sleep.

For what it's worth, there are a couple vendors of paired decentralized ERVs that alternate which one is supply and which one is exhaust and blow all the air through energy recovery cores that buffer both temperature and humidity. They're intended to be installed in holes in the walls, but it ought to be possible to fit them to windows or trickle vents with some creativity to operate them without any permanent modifications to the structure. In a climate with serious weather, energy recovery can substantially improve comfort and efficiency compared to using unconditioned supply air.

Yeah, if you can do it, I'm all for it!