[HN Gopher] Show HN: I built an under-the-door fan duct to lower...
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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.
Author : bizzz
Score : 34 points
Date : 2025-06-24 14:17 UTC (8 hours ago)
(HTM) web link (www.lepekhin.com)
(TXT) w3m dump (www.lepekhin.com)
| matthewfelgate wrote:
| Thanks for sharing, this is interesting to me.
| turtlebits wrote:
| 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.
| bizzz wrote:
| Good point for standalone houses! I live in an apartment, so
| everything you listed is backed by some concrete blocks. So,
| realistically speaking, the air in any meaningful amounts can
| only come through the window/trickle vent of the door.
| turtlebits wrote:
| You'd be surprised where air can leak in. Your house/building
| is not a closed system. You should assume that any/all wall
| penetrations will infiltrate air, via electrical
| wiring/conduit, through insulation, plumbing, hvac ducting.
| JayStavis wrote:
| I wonder what the market size for this is. If it were a real
| product that wasn't super ugly in the bedroom, we'd use it. My BR
| is ~1500 ppm with two sleepers in a 10x12 room, and opening the
| window isn't an option.
| bizzz wrote:
| Heh, never really thought there's a market for it. Though now I
| can imagine it being sold at some TV shopping channel. A
| solution to a problem you never knew you had.
|
| Anyway, I think there are plenty of people who do not want to
| open windows and still have fresh air. But the amount of people
| who can't modify their room or for whatever reasons don't want
| to open their bedroom door is bound to be much less.
|
| Now I'm curious, why don't you open your bedroom door? Me, I'm
| a light sleeper and other apartment dwellers will wake me up if
| I open the door.
| chipsrafferty wrote:
| Or just open a window, you'll also sleep better
| ecshafer wrote:
| Its 95 degrees outside. Ill take the AC.
| bizzz wrote:
| Yeah, if you can do it, I'm all for it!
| amluto wrote:
| 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.
| nancyminusone wrote:
| Software people will do anything but learn to use traditional
| CAD...
|
| Just kidding. But would you mind sharing what you find so
| compelling about CadQuery?
|
| As a mechanical person, these code to CAD tools make as much
| sense to me as suggesting you should write programs with a
| compass and straight edge.
| robbles wrote:
| I've used OpenSCAD for a few small projects. The main draw for
| me is avoiding all the "fiddly mouse stuff". I figure it's a
| trade-off between simple stuff being more complicated, and
| complicated stuff being easier to bulk edit and organize.
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