alt Hacker NewsFor anyone considering getting an air purifier, please do not get a Coway (or similar brands).
The air purifier market is full of garbage because consumers don't understand how these products work or what their tradeoffs are.
The root problem is that these products are designed the wrong way around. They almost all use custom-fit HEPA filters. That sounds great, HEPA is good, right? Except HEPA is really not good for household air filtering. HEPA is so fine that even air struggles to move through it. It's also far more fine than the common contaminants (dust and pollen) need. Because it's so fine, you need a VERY powerful fan to move any air through it, which means the purifier will be very loud.
Finer filters are not better. There are two things you want to optimize for:
1: CADR - clean air delivery rate. This is essentially how much air you can move through the filter per hour, multiplied by how much of the contaminant you can catch each time that air passes through the filter.
2: Volume - It doesn't matter how amazing your air purifier is if it sounds like a tornado. If you only run it for a few minutes before getting annoyed, the purifier is not doing its job. Every moment it is OFF it is not doing its job. Many purifiers try to use sensors to determine when to run the filter, but this fundamentally a flawed approach and just means you have low quality air 99% of the time.
The solution to these problem is a less-fine filter. For dust and pollen, something like MERV13/14 is absolutely fine. It will catch most of those on each pass, and because air moves through it so much easier - you can run the same air through it many times more in the same period of time. This results in an air purifier that is whisper quiet, keeps the air far cleaner, and can use off-the-shelf furnace air filters that are VERY cheap compared to custom-fit HEPAs which may stop being made the moment that purifier product line inevitably ceases to exist. (Note: This is mainly true in the US, said filters are harder to find elsewhere)
Combine MERV13/14 with off-the-shelf PC case fans (which have been optimized for decades to be as quiet and long-lasting as possible) and the result is an easily-maintainable, quiet, highly-effective purifier.
NOTE: People dealing with VOCs/odors need an entirely different approach that HEPA won't really solve either, for that you need activated charcoal which will run out almost instantly in the amounts common purifiers come with. You need a gigantic block of the stuff to last more than a month or two.
Replies
Thank you for this. I've been looking into buying air filters and would have made this mistake. (HEPA sounds good!)
I'm confused by your dust and pollen comment. What about PM2.5, is this mostly dust or are you not that concerned about this vs dust?
This is very helpful. Thank you.
Are there any example builds you could point me towards?
I don't think I've ever said this on HN, but: delete your post. It's nonsense.
Because it's so fine, you need a VERY powerful
fan to move any air through it, which means the
purifier will be very loud.
"For a purifier of its capabilities, the Mighty is notably quiet" - https://www.nytimes.com/wirecutter/reviews/best-air-purifier...
Alternatively, just take a glance at the ~30K reviews on Amazon. - https://www.amazon.com/dp/B01728NLRG
It doesn't matter how amazing your air purifier is if it
sounds like a tornado. If you only run it for a few minutes
before getting annoyed, the purifier is not doing its job.
Combine MERV13/14 with off-the-shelf PC case fans (which
have been optimized for decades to be as quiet and long-lasting
as possible) and the result is an easily-maintainable, quiet,
highly-effective purifier.
For a given CFM, with all other things being equal, larger fans (like the ones in Coways) are going to be easier than a bunch of smaller fans. Though, if using an array of Noctuas or similar, I'm sure it could be done.
Many purifiers try to use sensors to determine when to
run the filter, but this fundamentally a flawed approach
and just means you have low quality air 99% of the time.
The solution to these problem is a less-fine filter. For dust and
pollen, something like MERV13/14 is absolutely fine.
off-the-shelf furnace air filters that are VERY cheap compared to
custom-fit HEPAs which may stop being made the moment that purifier
product line inevitably ceases to exist.
But have you actually taken 30 seconds to look on Amazon and noticed the dozens of third-party filters made to fit the Coways? It's like buying Bose headphones. Yeah, you'll need to replace the earpads eventually, but they've been using the same earpads for like 15 years and there's an ecosystem of cheap 3rd-party versions... not 100% ideal, but also not a problem. As you note, maybe the situation's different outside of the US.
Any resources you could share here? I bought a Rabbit air filter years ago and it seems like it does fine. But since I did something similar to the OP here and started tracking my Awair air quality monitor in real time, I’ve noticed we have wild VOC levels in our roomy house and I can’t sort out what causes spikes, especially overnight. Some of it is probably due to the insulating and weather stripping mania I went through a while back and I’ve looked into getting an exhaust fan (whatever those things are called) to alleviate it but would like to know the source(s).