Comment by kbelder
3 years ago
No, a 10x difference would be between 0.9 and 0.09. What was given was about a 1.0005x difference. If you had a child that was .9005 meters tall and one that was .90005 meters tall, you couldn't tell which was taller without a precision ruler.
A E12 filter filters out 99.5% of particles above 0.3 microns.
An H13 filter filters out 99.95% of particles above 0.3 microns.
Assuming a volume of 10000 particles above 0.3 microns:
An E12 filter will leave 50 particles.
An H13 filter will leave 5 particles.
That's a 10x difference.
The only point the author was making with the 0.9005 vs 0.90005 example was that if you're only processing 10% of the air, then the efficiency of your filter doesn't matter. The entire section honestly would have been better without numbers, because they cause some amount of confusion and they don't really help make the point since it's obvious. If your room's air is recycled with outside air fully over the course of one day, and your filters take ten days to work through the volume of air in your room, then the efficiency of your filter doesn't matter.
That's it. Yes, one filter is 10x as efficient. It doesn't matter because in this example they aren't moving enough air relative to the room size/leakiness for it to matter.
Saying, "OK, but as a total percent of the air in your home at any given time, the difference is tiny" is … weird. It's still a 10x difference.
Using small numbers to make the difference look small doesn't hide that.
17 replies →
So? We're talking about practical effectiveness here. The difference really only matters if you only have one chance to filter the air, like the filter in a ventilation system bringing air into a cleanroom (the article goes into this).
Since the air purifier intakes and exhausts in the same space (meaning filtered air gets re-filtered), all the slightly worse filter means it that you'd need to run it for a couple more minutes to get the room down to a similar concentration of particulate per unit volume... So the difference in particulate concentration would likely not be anywhere near 10x at steady state, it would be much smaller (but depends how much air leaks into the room from outside, the particulate content of the outside air, the volume of air you're getting through the purifier per unit time, etc.)