By Jim Rosenthal
Much of the Eastern United States is covered with wildfire smoke from the massive fires in Canada. A very effective way to avoid this respiratory hazard is to keep the windows closed and use an air cleaner – like a Corsi-Rosenthal Box. One word of caution – use the right filters. We recommend MERV 13 or the equivalent.
Using a standard MERV 8 (mechanical) filter will just blow the particles around – especially those under one micron in size. Unfortunately, these sub-micron size particles are the ones that are drawn deep into the lungs and can cause the most damage.
To confirm this we did some tests comparing Corsi-Rosenthal Boxes using MERV 13 and MERV 8 filters. These tests were conducted in a 18’X20’X8′ chamber. An ultrasonic humidifier was used to generate particles. While this is not “wildfire smoke”, particles of this size move in essentially the same ways. A “control” level was determined and then tests for the 2 CR boxes were run.
The Corsi-Rosenthal Box using the MERV 8 (mechanical) filters had essentially the same 0.5 um particle count levels as the Control while the MERV 13 version had a 94% reduction. MERV 8 (mechanical) filters are really inefficient on sub-micron size particles. These results also suggest that replacing these MERV 8 filters in residential and commercial HVAC systems would be advised.