Air Purifiers as White Noise Machines
jefftk.com
jefftk.com
I’d never put two and two together until now, but that fan had to have been a major factor in some of the unexpectedly great naps in that room.
For most circumstances where someone would use
a white noise machine, this kind of small purifier
is all-around better.
Depends if you enjoy fresh air when you sleep or not. If you've ever monitored CO2 levels you know how quickly they climb in a closed room.
But, if you are blowing fresh air into a room, or have the windows open, the filtration effectiveness of these units approaches zero pretty rapidly. And these air purifiers aren't exactly free to run: they use ~50-100W of power and if you run them 24/7 you can expect to spend $100+ per year on filters.
So there's no perfect answer...
That sounds too high? An AirFanta 3Pro on "2" is 141 CFM at under 5W https://www.jefftk.com/p/running-an-air-purifier-on-batterie...
>if you are blowing fresh air into a room, or have the windows open, the filtration effectiveness of these units approaches zero pretty rapidly
Most people would just leave the window open <1", which keep CO2 down yet air purifiers still work well.
PM2.5: 2.6 µg/m³
PM10: 0.5 µg/m³
VOC index: ~97
CO₂: ~505 ppm
PM2.5: 10.8 µg/m³ (AQI ~46)
PM10: 17.5 µg/m³
VOC index: 122
CO₂: 572 ppm
PM2.5 - My impression is the health risks here are more cumulative exposure (and include things I'd like to go without in my life, like alzheimers) and a pretty straight line of "lower is better all the way to zero". The WHO's guideline is mean exposure of 5 µg/m³ so I guess I'd adopt that if I had to put a number on it. (But it's a mean, I wouldn't worry about briefly exceeding it)
PM10 - No real opinion (I'd rather worry about PM2.5)
VOC index - I'm not sure this is a standardized thing, but the version I've come across is an index relative to the average that particular sensor has seen in the last 24 hours. So there's no standard possible here.
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As for a gas range I would worry about NOX considering the studies with them causing and aggravating asthma. That said your CO2 levels are low so I suspect you might have sufficient ventilation that this isn't a huge issue for you (especially if that ventilation is in the form of a fume hood over your stove that you actually use).
CO2 is usually a proxy for air quality because outside is usually something consistent like 400 therefore deviation from that figure indicates staleness.
Besides which, proxy or directly high CO2 means you should ventilate...
having said that, it's possible they omitted what other gasses and %s they used for advantage. there could be some mitigation possible there.
Let's just say, if you look closely at the meta-analyses, all the effect size goes away if you omit one certain author....
If true, SAT scores should systematically vary by hundreds of points depending on which room you take it in. This is not observed.
I target 0 PM2.5, but this only necessarily makes sense as a target if you have the ability to filter your home's supply air. And a good vent hood should be able to avoid any detectable bump while cooking (although a vent hood without filtered makeup air may cause a bump due to increased infiltration of exterior air).
The instrument is pretty crappy - it has basically no calibration or, AIUI, long term stability. So you can’t really use it to characterize the chemical content of the air. What you can do is observe changes. I’m guessing the manufacturer wanted to avoid people getting confused by the absurd raw reasons, so they came up with a formula called “VOC Index” that HPFs the data. It will average 100 IIRC. You’re supposed to use it to notice events that cause changes - if it hits 170 every day at 2 PM them you can guess that something’s happening at 2 PM.
None of this is in the chip. It’s implemented by the driver. There’s an implementation in esphome, for example.
correct, that's not VOC sensors do. you need specific sensors for different gases for that. All VOC sensors are metal-oxide (MOx) sensors, i suggest reading on their supposed applications and uses.
But the actual behavior, at least for the SGP4x series, is so outrageously unstable and path dependent that you still can’t learn the value if that function of the gas concentrations. At best you get changes on timescales of minutes to a few hours but not on timescales of days.
again, correct. That's how they're supposed to work. If the air is very slowly getting worse, MOx sensors might not catch it.
That being said, what "very slowly" means depends on the sensor. For example, for Bosch BME680 (very good with 'organics'), you can set the tracking interval between 4 and 28 days (i use 28). Sensirion SEN66 (very good with 'chemicals') can have a tracking interval of up to 1000 hours.
https://sensirion.com/media/documents/296373BB/6203C5DF/Sens...
I’ve personally played with the SGP41, but I’m guessing the poster I replied to has the SGP40 because they didn’t mention NOX Index.
CO2 while occupied is generally under 750; I'd prefer to keep it under 700 but we also balance that with energy efficiency for that make-up air; I don't have an ERV, so we suffer a little there.
(We don't live by a freeway but - (a) Pittsburgh's air isn't great; and (b) the canadian wildfires were pretty bad here at times this summer, and that was what caused that 0.8 ug/m^3 pm2.5 spike).
We have, um, a lot of air filters left over from covid, though, so we're a little spoiled in terms of being able to manage AQI easily.
Typical concentrations of pm2.5 in outside air in winter time where I live are roughly 200-250 micrograms during the day, and into high hundreds (400-800) to thousands (highest I've seen is 3000) in the evening.
Yes, this is correctly measured by multiple sources.
This is what "isn't great" looks like, not your less than 20% of the latest WHO recommendation.
Unless it's just a mixup/typo.
The greater Pittsburgh region is #11 on the most polluted cities in the US by short-term particle pollution: https://www.lung.org/research/sota/city-rankings/most-pollut...
It's not Mumbai. But it's bad by US standards.
The thing that's not fully optimized are the CO2 levels in my house. As I've continued improving the air sealing in the house to reduce my heating and AC costs, it's something I want to address a little more in the future through active ventilation.
(Equivalent to saying you have more people under 2.5 years old than under 10 years old.)
I got one during Santa Cruz wildfires in 2020 and now the kids have a pavlovian reflex to sleep once that gets turned on.
Ikea makes an air-purifier table, which is a end-run around it being a useless box in the room when switched off.
It's fairly expensive, not as good as a purpose built one, but it blends into the average room pretty well.
But I recently got a Yogasleep Dohm Classic [1] and it really does sound better. Placed across the bedroom, with the two controls adjusted just... right... it makes that really nice water-rushing proper white noise sound. I do not like electronic ones at all, but there's something about this one which uses an actual fan + ports for the noise that is great.
I've also put it on a smart switch that I control from Home Assistant and this has made it even better. Specifically, I have an automation which gradually fades in some lights beginning 15 minutes before my alarm actually goes off [2]. I added turning off the white noise machine to the start of lights fading, and between the gradual light and sound change, I just sort-of wake up rather naturally a few minutes before the alarm noise starts.
(Just the lights were fine before, but the cessation of white noise adds a little more. And a "Bed Time" automation shuts off all the lights in the house, turns on the white noise machine, etc.)
[1] https://yogasleep.com/products/dohmclassic [2] https://nuxx.net/blog/2026/01/28/hue-a-better-sunrise-bulb/
There's plenty of higher end, actually really expense stuff out there. Austin Air is $$$ (but also a top performer): https://austinairsystems.com/collections/air-purifiers
It might not be guaranteed to help, but it sure doesn't hurt since it's cleaning the air anyway.
I have one blowing gently across my face while I sleep. It cools me down, and blocks out the highway noise.
But, if I'm not mistaken, the damage you speak of is caused by disrupting sleep. So the idea is that if a white noise generator can drown out the interruptions, it helps you sleep better. There are studies that say noise doesn't help, and there are those that say it does. And it's all real-life medical research, so pretty unreliable. I found one controlled study (https://doi.org/10.1093/sleep/zsag001), but it's small, and only 7 days, and it's in a lab, so not guaranteed to translate to normal conditions either.
And don't ignore the placebo effect. Perhaps believing that pink noise helps is sufficient for some.
Perhaps a better recommendation is good ear plugs.
I expect there are more complex stress response mechanisms at play here, not just disturbed sleep.
>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.
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
I like silence.
I consider noise from things like a refrigerator, or a computer case fan, to be distracting, and a reduction in the quality of my environment.
White noise is still noise, and there's no noise like no noise...
The naming isn't great in the competition, but: Alpine, EarGasm, EarPeace, Loops are significantly better. Recent Alpine reviews suggest a material change - so maybe not them (haven't tried the new ones). They all come in different editions which is mostly about which frequencies they block/allow through.. loop is trying to push the price boundary (probably avoid, especially their "active" line).
All better than basic fluorescent foam earplugs though, easier to use and better sound blocking (the good audio ones allow you to speak/hear voices at close to normal volume in front of a 90dB sound stage)
Where I need extra help is with VOCs in certain locations. Like, in or near bathrooms. Or the cat litter boxes. IQAir does sell their GC line for that, and we have a couple of those. But the activated carbon filter media is super expensive. And these things are huge. Like, bigger than a dorm refrigerator.
So, I welcome an alternative that does VOCs well.
I grasp that such an approach might draw unfiltered surrounding air along with the filtered stream of air, and imagine that it would likely be easily overwhelmed by a steady supply of exceptionally polluted air (wildfire smoke or simply a heavily polluted urban area), but I still would be interested in knowing if the compromise never overcomes a level of placebo effect, or if there's a point where it actually achieves measurable benefit (both in efficacy and portability—like a even more compact and directional version of the Corsi-Rosenthal computer fan solution.)
These directed-air "personal models" make a lot of sense to me... at least in theory. I haven't seen them properly tested.
The big air purifiers work great.. if the room is closed up. But their effectiveness approaches zero if you have the windows open or otherwise have unfiltered air entering the room. Which is kind of important, if you don't enjoy breathing in sky high levels of CO2. (If one's allergies are bad enough, or a wildfire is raging outside, CO2 might of course be preferable to particulates)
https://air-fanta.com/products/airfanta-4lite
However, testing seems to show that the clean air flow is neither wide nor far; it would only be effective right next to your face and you can't really move:
https://www.reddit.com/r/Masks4All/comments/1di1n4t/can_a_po...
There aren't a lot of use cases for it.
There might be some to your dog, on the other hand. Anecdotal, but my dog went deaf pretty early and he sleeps in a room where I run an air purifier all night. Not sure if there is correlation or causation there but that's my little anecdata.
How do y'all track air quality in your home?
I also like the fact they offer a discount if you buy it as a kit to be assembled (it's very easy to put together).
Maybe it was something from manufacturing that was irritating your throat? Idk.
Unfortunately, the replacement filters cost way too much. The IQAir unit itself, though, is still working great after 15 years.
I bought the Ikea (FÖRNUFTIG) because I was worried that lesser known brands on Amazon might go out of business, making it hard to find replacement filters later
I combine it also with a dehumidifier because I live in a place with a lot of humidity.
The point stands. If you care about this, it's a personal choice whether that comfort is worth ~20€. I would wager many people say it is.
I prefer having quiet air filters that I can run all day (based on air quality) instead of noisy ones I only use at night.
I have one in the bedroom. On low, I barely hear it during the day (extra ambient noise from outside) but at night the white-noise is subtle but effective. That said, I don't like "loud" white noise, just a quiet hum.
Housefresh, which is a criminally underrated review channel btw, recently did a comparison of PC fans for this purpose. The Thermalright TL-14C family came out strong in the "Silent" category, with the best ultra-quiet 24/7 fan speed performance. This comes at the cost of slightly worse max speed CADR vs the venerable Arctic P14.
I still haven’t seen anything else that can compare to IQAir HyperHEPA filters. They use these things in hospitals.
Turning them up to med/high would just cause too much airflow.
I agree big fans moving slowly is better all else equal, and something AirFanta-like that used a 12" fan could be even better.
For sleeping I prefer rain sounds though
>removes smoke and infectious particles
Where do people live that they need to remove such things, 18th century London?
SF Bay Area during the summer fires of a few years ago
So you got responses about smoke and dust which are a very very common air quality problem.
I guess that's too subtle for HN. In the future I will be sure to emphasise when my ANDs are boolean.
Wind blows smoke around. There are currently fires in northern Michigan that are affecting the air quality in Chicago, which is 350+ miles away.
My allergies became generally better at all hours just from sleeping in super cleaned air.
Why? Reducing baseline inflammation perhapse? Maybe decreased inflammation during sleep helps too, improved breathing? idk. Whatever it is this organism seems to prefer it.
Even when exposed to allergens during the day the run up to sneezing is much slower or doesn't happen.
https://commons.wikimedia.org/wiki/File:Wildfire_smoke_Wyand...
It just looks like fog, but it is smoke, and the sky has an unusual orange color. Smells and tastes like you are standing in the path of a campfire, but you can't move out of the way. It irritates your eyes and throat if you spend more than 20 mins out there. You can go inside, but if the building you are in is leaky, it will smell like smoke inside there too.
The actual fire was hundreds of miles away. You can try driving in any direction for hours and not be clear of the smoke. Still, compared to other areas, this is barely worth complaining about.