Oct 31, 2026
Achim Haug
I wanted to see how simple I could make a positive-pressure fresh-air system. I believe this is about the simplest PPS design possible: a popular cylindrical replacement filter, a standard four-inch duct fan and one small 3D-printed adapter. Both the filter and fan are readily available.
Unlike a recirculating air purifier, this setup does not filter the air already inside the room. Instead, it pushes filtered outdoor air in, flushing dirty indoor air out. With sufficient airflow and a suitable installation, the resulting positive pressure also helps reduce unfiltered outdoor air leaking in. This fresh-air exchange can also lower the CO2 that builds up in occupied rooms, something a particle filter alone cannot do.
The fan and filter come to roughly US$50–60 at the prices quoted in the demonstration, before printing, ducting and installation.
In my initial check with an AirGradient Go, the PM2.5 reading fell from around 17 µg/m³ outdoors to approximately 0.5–0.6 µg/m³ in the filtered outlet air stream.
We will publish the video and full blog post soon, showing the parts, assembly and initial checks.
Read update
