There was some talk on here during Covid about the feasibility of making all structures up to BSL4 standards. Seems kind of nuts, but it would certainly contain a lot of biosafety threats. With AI it now seems borderline urgent.

AirFanta creator Adam Wong has a version using a 3D-printed adapter to 8" circular duct.[0]

In newer builds he places the purifier box indoors and simply reverses the orientation of the fans and filters. This keeps the box protected from weather, and the duct can be run in such a way as to keep out rain or dripping.

The AirFanta is actually rated as EPA E11 (95%) not HEPA H13 (99.97%), so if you're trying to keep out everything in one single pass like a clean room then AirFanta might not be best. It may be a good idea to check the real-world interception performance with a particle counter.

[0] https://x.com/Engineer_Wong/status/2034098395376455946

https://www.reddit.com/r/crboxes/comments/1ef3dly/positive_p...

I live in an apartment over a busy road, and my building doesn’t have forced-air ventilation to the units, so I need to pull in fresh air somehow. Just leaving the doors/windows open results in black spot accumulating in the carpets (and is probably why my cat developed asthma.) regular air purifiers (we have two) only do so much.

What ended up making a difference for us, is buying an industrial air scrubber, of the kind construction sites use to clean the smoke and dust (and mold, and asbestos, etc) they’re generating out of the air before it gets vented outside (see e.g. https://a.co/d/01lTtyuZ); and plumbing this machine into our apartment in reverse: putting it out on our (covered) balcony, with it exhausting the “scrubbed” air into the apartment. (I made a little sliding-door shim of the type people use to pipe portable AC units outside, just with the hose on the other side.)

Generally works great. We run it on a very low speed, so it’s surprisingly quiet (or at least no louder than other fans we have for air circulation.) The pre-filters get absolutely caked with exhaust and road dust after ~2wks, and start to let through an odd stench at that point, so we’re actually replacing those faster than even is recommended for the industrial use-case. But the actual main HEPA filter inside the unit seems to last longer than the industrial usage would predict.

An ERV with HEPA filter may be a better, less improvised option. Most systems can be adjusted for positive pressure, although the intent is balanced airflow.