A HEPA filter must remove 99.97% of particles at 0.3 micron. Each air purifier is tested using a Met One laser particle counter calibrated to measure 0.3 micron sized particles per cubic foot of air.

Ambient Particle Count: 1,479,100 / cubic foot
This is the number of particles in the air before filtration, giving us our benchmark number to compare results with. True HEPA results need to be under 443 particles after filtration (99.97% efficient at 0.3 microns)

Filtered Air:
The particle counter is then arranged so that it is taking in 100% of the outflow air from the HEPA filter. The results show how many 0.3 micron particles escape the HEPA filtration process.

The Results:
Filtered Particle Count: 0
(can't get much better than that!)

Click here to see an actual test done with a laser particle tester (includes video)

Click here for a complete sizing chart with all portable systems.

Click here for more detailed info.