Comment by Lazare
3 years ago
The Wirecutter article is pretty bad though:
> But it isn’t a true-HEPA purifier, or a very powerful purifier, period. It’s designed to capture PM2.5—that is, particles 2.5 microns in diameter and above, in contrast to the 0.3-micron HEPA standard. That means it’s optimized for larger airborne particles such as pollen and mold spores, rather than for very fine particulates like wildfire smoke, as HEPA filters are.
First, "True-HEPA" has no legal or scientific meaning, so that's not a great look.
Second, and a minor point, the 0.3-micron standard related to the US HEPA standard, not the EU one. It is true that acording to IKEA it doesn't meet the EU standard for HEPA (barely), but we don't know whether it meets the US one. Eliding the difference between different standards isn't helpful
Third, and more seriously, PM2.5 means particles 2.5 microns in diameter and smaller, not larger, and PM2.5 filters are designed to capture particles 2.5 microns and smaller. Mold spores are mostly 4 to 20 microns, pollen averages around 25 microns, so while the IKEA unit may or may not be good at filtering wildfire smoke, it is not optimised for mold and pollen and is probably terrible at it, so that entire line of analysis is just backwards.
That's a lot of errors to pack into a short passage, and it really gives the impression that the author doesn't really understand or care about the topic.
As for CADRs, the linked post digs into the tests pretty well, and I agree with the conclusion - they're not credible. Note specifically that they get a variance of over 2.4 times between tests, and in somes cases measure a CADR vastly higher than the manufacturers claimed CADR. If you're reading a benchmark of a new graphics card and someone ran a benchmark twice and got 100 FPS once and 240 FPS the second time, and they just shrug and pick the number most convenient for their conclusion, you'd probably think something was up.
(That being said, the linked post is a bit iffy too. I'd call out specifically that they could have done a better job of acknowledging that US HEPA standards are a thing, that PM2.5 filters are a thing even if they're not a standard, and that technically E12 filters aren't HEPA, even if that's an arbitrary distinction most people ignore. But they're quite right that the Wirecutter - on the review of the IKEA unit - does in fact seem to think air filters work like sieves. Certainly I can't think of any other explanation for that passage about PM2.5 being good for pollen!)
> Second, and a minor point, the 0.3-micron standard related to the US HEPA standard, not the EU one. It is true that acording to IKEA it doesn't meet the EU standard for HEPA (barely), but we don't know whether it meets the US one.
Wikipedia cites this statement:
> Common standards require that a HEPA air filter must remove—from the air that passes through—at least 99.95% (ISO, European Standard) [...] of particles whose diameter is equal to 0.3 μm
to "European Standard EN 1822-1:2009, "High efficiency air filters (EPA, HEPA and ULPA)", 2009". Have they made a mistake? ( https://en.wikipedia.org/wiki/HEPA )
The same sentence goes on to note that the American standard is similar, but more strict, requiring filtration of 99.97% of 0.3 μm particles. As such, it is not possible to meet the American standard while failing to meet the European standard, so there's no need to discuss the American standard separately.
From the same Wikipedia page:
> The specification used in the European Union: European Standard EN 1822-1:2009, from which ISO 29463 is derived,[4] defines several classes of filters by their retention at the given most penetrating particle size (MPPS): Efficient Particulate Air filters (EPA), HEPA and Ultra Low Particulate Air filters (ULPA).
The Wikipedia citation goes to a specification which is, annoyingly, not freely available, but Google seems to confirm that Wikipedia is correct. Many sources confirm that EU standards measure penetration at the MPPS, I can find nothing suggesting they use 0.3 microns for anything.
I think the introduction paragraph for that Wikipedia page is simply wrong, and it's conflating two different standards. The actual section on HEPA specifications, however, is much clearer.
Technically, if retention at the most penetrating particle size is 99.95%, then retention at the 0.3 micron level is at least 99.95%.
But obviously measurement is not actually done at the most penetrating particle size, because retention at that size would be indistinguishable from zero. It isn't clear what they mean when they say "most penetrating particle size".
> defines several classes of filters by their retention at the given most penetrating particle size
If the MPPS is given... what is it?
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