By Jim Rosenthal
Many people have asked for a smaller version of the Corsi/Rosenthal Box Air Cleaner. In the spirit of the “open source” cooperative approach there have been several versions pictured on Twitter. These excellent examples inspired me to build one myself. Here is the result – a Mini-Corsi/Rosenthal Box!
The fan is a readily available 9″ box fan ($21.99). The filters are MERV 13 – 10″X10X2″ (9 1/2″X9 1/2″X13/4″) from Tex-Air Filters ($10 each). We used white duct tape.
Mini CR Box efficiency (as measured with a Lighthouse Handheld 3016-IAQ) results were the following:
| Particle Size | Ambient | At Fan | % Efficiency |
| 0.3 um | 2824500 | 1443000 | 48.91% |
| 0.5 um | 458200 | 202500 | 55.81% |
| 1 um | 26800 | 8200 | 69.40% |
| 2.5 um | 1200 | 200 | 83.33% |
| 5 um | 200 | 0 | 100.00% |
| 10 um | 100 | 0 | 100.00% |
These filter efficiencies are comparable to other test data and other measurements taken with full size Corsi/Rosenthal boxes.
This Mini Box Fan has three speeds – Low, Medium and High. Here are the test results for each speed.
| Speeds | FPM at Fan | Noise Level | CFM at Fan | CADR est. Smoke | CADR est. Dust |
| Low | 385 | 45 dB | 188 | 75.2 | 131.6 |
| Medium | 454 | 49 dB | 222 | 88.8 | 155.4 |
| High | 480 | 52 dB | 235 | 94 | 164.5 |
CADR is calculated on the basis of CFM times 0.40 for smoke and CFM times 0.70 for Dust.
All in all, the Mini Corsi/Rosenthal box is an excellent option for smaller rooms like individual offices, small bedrooms, nurseries, hotel rooms and other areas where the full power of the regular CR box is not needed. It is relatively quiet – yet powerful enough to move a substantial amount of air – definitely a viable DIY option. It works!