One of the best air purifiers you can get (linked in the above writeup) uses PC fans and a custom controller where you can control the speed/volume: https://housefresh.com/best-air-purifiers-we-tested/#2-best-...
https://makerworld.com/en/models/2470181-nukit-tempest-euro-...
If you were actually looking for an answer, the AirFanta's creator Adam Wong recently answered a question about this:
Production costs include raw material procurement (my fan and filter suppliers are happy, since each machine requires four fans and four filters—more than they supply to other brands) and labor assembly costs. In addition, there are shipping costs from China to the US, Europe, and other regions, warehousing fees, and last-mile delivery fees. For what it's worth, in the US, shipping this 17 lb box already costs about $18. Also, Shopify and credit card channels take just under 5%. We also hope to promote on Amazon in the future. Estimated advertising costs are 20%, and Amazon charges another 15% in fees, so that adds up to 35%. If you're not in this business, it's normal not to know these expenses. But I have to say, the costs are much higher than they appear on the surface.
120mm high static pressure fans are £7 (so £28), an AC power-supply fan controller £11. IKEA filters are £3 each, so £12. So we're looking about £50, be generous and chuck in another tenner for 3d printed ABS and screws etc. £60 all-in at 1x retail/Amazon prime prices, delivered to my house.
If I was doing this at scale I am sure I could get lower than the retail Amazon prime prices. But even if I couldn't this is about half of the £130 RRP. Yes there are labour costs to assemble this but this is not exactly a swiss watch and looks like it comes flat packed anyway?
Do note that the AirFanta uses 140 mm fans, and IKEA filters are E12 vs E11 so the airflow would be less optimal[1], but hey who's counting. ;) Also I envy how cheap your IKEA filters are; in the US they're $18 & $25 now.
[0] https://cleanaircrew.org/box-fan-filters/
[1] https://twitter.com/Engineer_Wong/status/1899144721710408038
>Of course, the problem with this is you are just spending more money on filters, which is the expensive part.
For cost over time, twice the filters means twice the replacement interval, so the additional filter cost cancels out.
I'm sure it works but like any engineering decision it has pros and cons.
>you get to look at any collected dirt
However, if you really don't want to look at it, you can always flip most DIY designs inside-out so the fans blow in and dust collects on the inside instead of the outside! This doesn't clean the room quite as efficiently, but if the appearance of dust is a major concern that should be a fix.
Flipping the fans isn’t great because then you have to clean the fans, this is why draw-through is the standard configuration. Also many designs like this rely on negative pressure to seal properly or even stay together. You might just have the lid take off like a helicopter.
All the purifier companies realized they make more money selling overpriced filters, so $60+ for the OEM filters is common nowadays. Despite it just being a standard HEPA filter cut to a specific size.
Airfanta 3 Pro filters (four) - $57
Coway Mighty Filter - $60
Coway Mighty2 Filter - $70-$80
I'd be concerned about the availability of filters after a few years. Some of these companies have been changing their models and filter type every year to add some nebulous feature. Others just go out of business.
HEPA media itself is a commodity and aftermarket filters (and the BOM cost to the OEM) tend to level out at whatever rate is minimally profitable per area of filter media.
The upfront cost of this device is high for what you get, because you're mostly buying filter media. The device itself is not much of a polished product. I'm sure it works fine but I wouldn't want one in my living room.
I leave them on setting 2 (unless someone is sick or we're having a lot of people over), and we get ~425 CFM for about $40/y in power (~5W each).
The trick is to use high-airflow MERV 13 filters (ideally 3M 1900, which has high pleat count and low resistance) instead of high-resistance HEPA filters, so axial PC fans can generate enough pressure.
For a standalone air filter which is pushing the filtered air into the same room its drawing from, we can assume reasonably good mixing of the intake and exhaust air. Thus to be equivalent to a HEPA-filter it only needs 1/3rd more airflow... Which really isn't much.
This doesn't follow for a a fancier setup where you're taking dirty air and blowing it into a cleanroom or something... but that's not how we're typically using household air filters.
And that really does make a huge difference to someone who has allergies.
IQAir does HyperHEPA, and they go down to 0.003 microns (so, a hundred times smaller, down to the size of viruses), and they capture 99.5% at that size. That’s why they’re used in hospitals.