Timonsku's 3D-Printed Two-Filter Design Is a Smaller, Cheaper Take on a Corsi-Rosenthal Box

Pseudonymous maker "timonsku" has created a more compact take on the Corsi-Rosenthal air filter, designed to cut both the cost and the footprint — by putting four computer fans between two heating, ventilation, and cooling (HVAC) filters with a 3D-printed framework to hold everything together..

"[I] wanted to see how cheaply and easily you could make a Corsi-Rosenthal style air filter with just two filters," timonsku explains. "In the original the four filters make up the main structure. That doesn't work with just two filters. So [I] came up with 3D printed nubbins that give the sides structure + plates for the PC fans. Its super quite, can barely hear it while having similar air pressure as the commercial units at a loud medium setting."

The Corsi-Rosenthal Box was developed by engineers Richard Corsi and Jim Rosenthal during the COVID-19 pandemic, as a way to deliver low-cost yet effective indoor air filtration en masse. It's an air filter cut down to its bare essentials, and constructed from readily-available parts: four off-the-shelf HVAC filters form the sides, with optionally a fifth as the base, with a box fan on the top. Tape and cardboard fill the gaps, and the result is a high-efficiency air filter that can hit 850 cubic feet per minute at a cost one-tenth that of commercial equivalents.

A traditional four-filter box, though, takes up quite a bit of room, and four filters are twice the price of two — which is where timonsku's more compact take on the concept comes in. Two filters make up the wider sides of the filter, while the narrow sides and base are simple tape. Rather than a square box fan, the top uses a framework that houses four 120mm PC case fans — though timonsku suggests you could add more fans on the sides if you want higher airflow.

"Total cost is like €20 [around $220] for duct tape, 5× fans, and ASA filament excl. filter cost which varies," timonsku calculates. "This works with any 1" 3M MERV filter, no matter what dimensions. Four typical [quiet] 1,100 RPM [Revolutions Per Minute] PC fans give you around 220 CFM [Cubic Feet per Minute]. Use fans that have the big old four-pin Molex connector because those can be daisy chained without additional hardware."

timonsku has published STEP files to GitHub under an unspecified license; more information is available on the maker's Mastodon post.