Experiments on a $50 DIY air purifier you can make in 30s | Hacker News Reader

Experiments on a $50 DIY air purifier you can make in 30s

dynomight.net

62 pointsthrowup23865 comments

Sadly the state of California bans simple box fans + filters from being sold. For example if you try to buy a "Lasko Air Flex Steel Portable Home Office 3 Speed Air Purifier Machine Box Room Fan with Manual Ergonomic Control Knob and 6 Foot Cord, White" from Amazon you will be greeted with this when you try to order:

"""This product does not meet California air cleaner regulation requirements, and cannot be shipped to California"""

This is essentially like the video, but a slightly beefed up box fan to handle the extra load from the filter. It also takes standard household furnace filters. People have tested these and they totally work.

For a state that often has horrific air quality due to wild fires it's total BS you can't quicky order something like this off Amazon in a pinch.

Reading [1] about the regulations, it sounds like the only requirement (for self contained air cleaners) is that it has to be certified, and can't produce ozone. That seems pretty painless, and I would like the comfort of knowing that if I buy an air cleaner, it actually does what it says. Same as masks should have testing requirements to show efficacy.

[1] https://ww2.arb.ca.gov/our-work/programs/air-cleaners-ozone-...

Re masks - unless you buy them and wear them because of the rules, and not because you want to achieve some physical/medical effect.

I mean you can put regulations on anything to make it sure it is doing what it is supposed to be, right?

The spirit of the regulation is to make sure it is not emitting ozone like this ozone filter-less purifier: GreenTech GT-50.

It may be "painless" but if it costs $X per unit to certify and they make $x-.01 per unit, the company isn't going to sell that in CA.

The harm caused by the lack of a super cheap and effective air filter, especially in CA where we can get smoked out for weeks due to fires could be greater than the harm reduced by the regulation. Especially when it is obvious that this in now way could emit ozone since it is just a fan and a filter.

> I mean you can put regulations on anything to make it sure it is doing what it is supposed to be, right?

Yes, and when it comes to selling health-related products, the standards are higher than, say, entertainment devices. For very good reason.

> The harm caused by the lack of a super cheap and effective air filter, especially in CA where we can get smoked out for weeks due to fires could be greater than the harm reduced by the regulation.

That's not clear to me. I know lots of people with air filters, and they all chose them based on aesthetic judgements. I doubt any of them would've acted differently if it was $5 cheaper (from certification)

Also, you can still just buy a box fan ($30) and tape a filter ($10) to it and hope for the best in terms of air purification. You just can't pay someone else $70 to sell you that, unless they run a test to prove it works. Doesn't seem like a big deal.

I genuinely don’t see the problem.

I live in CA. I can go to the store and buy a box fan, and I can buy them online and cheaply. I can buy little clips for holding filters on box fans. I can buy MERV 13 filters at any hardware store or online, and the ones in store are sold at competitive prices and are from real brands that aren’t making up the specs. I can buy actual air purifiers from many vendors, including IKEA, which sells genuinely excellent purifiers.

So what if I can’t buy that hilariously overpriced LASKO kit? I dislike nonsensical CA regulations about as much as anyone else, but this example is silly. I can spend less money to buy a LASKO box fan, a nice set of clips to hold a filter on, and a better filter. Although Amazon is really not a fantastic place to buy just one or two filters — Home Depot or ACE is better.

> """This product does not meet California air cleaner regulation requirements, and cannot be shipped to California"""

From your description, it sounds like you are referring to a product that is advertised as an air purifier in spite of not offering any assurance that it actually purified air at all.

California has set a low bar on what can actually be claimed to be an air purifier and sold as such. Your example product failed to meet that bar. Therefore, it cannot be commercialized based on claims that it has not backed up.

Sounds to me like society is working. Snake oil is not excusable in this day and age.

A box fan with a HEPA filter stuck to the back of it has been proven to work reducing PM 2.5. The EPA seems to think they are OK:

https://www.epa.gov/air-research/research-diy-air-cleaners-r...

It's unreasonable for a box fan that can accept a standard filter on the back cant be sold. It's completely safe to use and not a scam at all. Buying this model means you don't have to duct tape the filters on. Also the model is designed to tolerate the extra load from the filter.

> A box fan with a HEPA filter stuck to the back of it has been proven to work reducing PM 2.5. The EPA seems to think they are OK:

You are free to MacGyver whatever you want.

The moment you want to sell something you put together as a product that does something, you need to make sure that you are not defrauding the public. If your device really does what you claim it does, just subject it to tests to assure everyone.

California is saving you from buying an overpriced absurdity with unspecified performance.

Just buy a box fan and a filter. You’ll need to know how to buy filters anyway so you can replace them.

This is literally what the product I am talking about is. It's a box fan that has a filter holder on the back of it. It uses a standard furnace filter size. Keeps you from having to tape the filter on, etc.

This thing?

https://www.amazon.com/Lasko-Portable-Purifier-Machine-Ergon...

With a MERV10 filter? Advertised as removing smoke?

Here is some actual MERV data:

https://www.epa.gov/indoor-air-quality-iaq/what-merv-rating

MERV 10 is not guaranteed to remove sub-micron particles at all. You need at least MERV 11 for that. [0] Having personally tested some filters in wildfire smoke with a little handheld particle counter, I believe in actual specs. If there isn’t an actual spec referencing a defined standard, then it does not matter how many platitudes about smoke are given — the device is unlikely to work.

[0] And you probably want MERV 13-16 to get to the air purifier sweet spot where flow times removal rate is large and where cost is reasonable. But if you’re going to err, err in the direction of HEPA so that particles actually get removed.

most filters remove large and small particles. its the mid size that the good filters get.

Hmm, I recall an EPA chart showing expected performance of different MERV classes versus particle size that had the lower classes staying at zero for very small particles, but I’m not seeing it right now. But I found this — start at page 71.

https://ordspub.epa.gov/ords/eims/eimscomm.getfile?p_downloa...

You do want the higher MERV classes to get decent performance.

this linked article has a bunch of info https://news.ycombinator.com/item?id=31812259

It looks like there’s an opening for someone to market one of these as a scientific instrument for the outdoor collection of airborne pollutants.

There is also an opening for someone to market this exact product exactly the same, but just undertake the testing to prove it actually works as advertised to comply with California law.

As a state where air quality is a major public health concern, it seems very reasonable for the regulations to protect consumers from being sold scam products that do not actually filter the air. I understand this concept is well tested and proven, but I think we're all familiar with the general counterfeit product issues on Amazon and I would be 0% surprised to get a fake of even such a simple design.

It would be more reasonable for the government to protect its citizens in a state where air quality is a major public health concern.

I see articles pop up like this all the time on HN like it's some kind of revelation. All you need to remove particulate matter from your air is a fan that pushes air through an HEPA filter. You dont need wifi, bluetooth, lcd screens, or a phone app. All those things plus some fancy instagram marketing is tricking people to spend $700+ on an air filter.

>All those things plus some fancy instagram marketing is tricking people to spend $700+ on an air filter.

I think there is also the middle ground of spending about $150 on an air filter, because the ones from Ikea and Bluair look and sound much nicer in my home than a box fan with a HEPA filter duct-taped to the front.

I don't mind the repeated breathless excitement over it. It feels very on-brand for hackers to get excited about discovering a cheap and ugly DIY version of a commercial product and apparently miss that not everyone wants one in their kitchen.

That, and ignoring the other downsides of a hacked together device - noise and power consumption.

The Winix 5500/5300 are pretty great. Super quiet and use 5-8 watts at setting 3 of 4. Box fans can't really compete there.

Yep - I got a Winix 5300 ~3 years ago and it's been great. Nice and quiet, low power, and the squirrel cage blower in it is really good (which is rather important - you need a lot of static pressure to push/pull air through a HEPA filter and box fans just aren't really up for the task at low levels).

Despite appearing almost identical, I haven't had good luck with the Winix C535. All 3 had poorly balanced blowers that either ticked or rattled, which wasn't the case in the 5 5500/5300 I've owned. It's a pity because they're super cheap at Costco.

It's not trivial though - it's not easy to 'push air through a HEPA filter' - you need to shop for a motor, blades, and filter more than simply fan (comprising motor and blades) and filter really. Or at least you need to be aware and get a suitably beefy fan - I think $50 is a hard budget to hit just for that reason. Or at least it is if you don't have easy access to cheap 'box fans' that are for some reason so prevalent in North America (what's their usual use?).

You can spend a lot of money on just a fan, it's not just air purifier marketing nonsense.

Unsure about the entire US... For my area they were called "window fans" in previous times. Before air conditioning was prevalent, you'd use these box fans, placed in the window, to circulate air to provide a more comfortable environment.

In years past, the fans were beefier than the current generation. They also used metal fins. Speaking into one made a vaguely similar effect to speaking Like Darth Vader. It was entertaining as a child.

Agree! However article is comparing to a $100 option and he spent about $60 on DIY supplies. The price differential is small enough that nobody should DIY. The convenience of having an auto-sensing device that turns on and off when based on changes to air quality is well worth the extra. As is the ultra low noise operation and added aesthetics.

> nobody should DIY

> nobody should DIY for price reasons

FTFY. Lots of reasons to DIY other than price :)

The DIY option should have been closer to $30 if they used a 20x20x1 filter (~$10), which fits perfectly on a box fan.

Also, I have yet to find an $100 air purifier that has a high enough CADR to filter a large living room.

He's comparing a $100 option that does not have an auto-sensing device to a $54 option (that also doesn't have a device.)

This is pointed out by the author:

> Some (more expensive) commercial purifiers have air quality sensors built in and automatically turn on only when needed.

So in this case, you still have to manage fan speed yourself. Overall the bigger picture would include cost of filters over time, as well as electricity (which may be in favor of the commercial unit.)

And finally, you have to consider the dollar value of aesthetics!

IDK if that's true, I have one that I paid about $100 for and has sensing. It's quite nice and I basically never know when it's on it's so quiet. It also came with a reusable/washable filter, so I've never had to replace it after about 3 years of use now. Any ways, I DIY a lot of stuff, but there's not enough interest in this one unless you're just a glutton for frugality or find some interest in this particular project. My point was that for most people this would be a negative time value of money for inferior outcome; which I think are why most people DIY things... so they can afford better or learn something. (There is no learning when all you're doing is strapping a filter to a box fan.)

I built a big DIY one and then immediately bought a non-DIY one for my bedroom.

The filters are going to cost a lot more, but it looks a lot nicer and I don't have to think about turning in on and off - it's runs on auto.

You don't even need a HEPA filter. A lower grade filter will do fine as well for recirculating air: the idea is to reduce particles by passing the air of the room again and again through the filter. If you have a air source that has more particulate pollution than the sink a better filter makes more sense.

None of these articles allude that you need any fancy tech to filter air. You're preaching to the choir.

The people buying $700 air filters are typically not very tech or DIY inclined, although HN does tend to fall for "expensive is good" kind of marketing once in a while (most notably - Apple)

Can you show me a Windows laptop that has Microsoft telemetry disabled permanently?

Expensive _is_ good […] once in a while. Most notably, Apple.

I dont think anyone is confused about this.

Do you want to see/measure/track air quality? Do you want to be able to remotely control the purifier? Do you want a device that looks good? Do you want other features like heating/rotation/etc. Those are the reasons you might buy one...

Yeah, but if it doesn't have all that fancy stuff then the geniuses here couldn't lock you in to Air-As-A-Service!

These articles have been popping up ever since the cheap air quality sensors started showing up that everyone and their dog hooks up to their raspberry pi like it's some grand revelation. I wonder if the measurements also have a logarithmic quality making the change in absolute values after turning on a filter appear more impressive.

Skip the HEPA and use a MERV 13-16 filter. You’ll get better results at lower cost.

One thing the article doesn't seem to mention is noise. I've found that the "actual" air purifiers seem to be much quieter than box fans. Perhaps if you had greater control over the box fan's speed you could get the noise down to a comparable level, but I doubt the cheap type of fan used in the article is capable of such a thing.

Yep, the DIY may work in an emergency but there are good reasons like noise, size, and power usage to get a commercial product if you're going to be living with it.

The layout of the purifier is important in a crowded space - the DIY requires open space both in front and behind for good airflow, but the commercial ones have a front intake but vent straight upwards, so you can shove it against the wall. No one is going to put their air purifier in the middle of the room away from other furniture.

Indeed, the thing that keeps me happy with the Coway 400 I've got is the very small power use when particulate is low and the automatic ramp up when it goes high. My fan I keep near my bed for my own comfort pulls 30 watts. The Coway pulls something more like 5 watts in low use. Expensive up front but low ongoing cost and 4 years running now.

The primary perk for a more expensive unit is the ability to modulate that fan speed based on the particulate level in the room, IMO. I've got a couple of units that I paid ~$140 for which can step their fan speed up and down based on the measured air particulates. Most of the time, they're running at low speed and are effectively silent - just cycling the already-pretty-clean air in the room at a low rate - but if something causes a spike in particulates (say, cooking), they'll crank up to a significantly higher speed (and level of noise) until the air is cleared.

If you've got a box fan running all the time anyhow and don't mind the noise, though, strapping a HEPA filter to it makes plenty of sense.

You can do better with a Corsi–Rosenthal Box:

https://en.wikipedia.org/wiki/Corsi%E2%80%93Rosenthal_Box

The gist of this post is that ‘better’ isn’t necessary; any will suffice. So long as there’s airflow traveling through the filter pleats, your air will get cleaned.

If you’re in a wildfire scenario, you should — if you can afford to and can still find and purchase the parts — absolutely go the extra mile, because you need to maintain a filtration level sufficient to overcome the particulates brought in with outdoor air.

Regardless, any time you have a box fan, just tying a filter to it will clean your air as effectively — but not as rapidly — as a commercial filter, under typical home scenarios.

They are indeed awesome and I made one with a simple box fan. It works great but it’s really loud. We can’t really have it on when company comes over.

We got one of these instead and have been really happy with it. Pros: super-quiet low-energy computer fans. Uses standard air filters you can buy at Lowe’s. Cons more than a box fan.

https://www.cleanairkits.com/products/brisk-box

They are awesome and cheap but take up a lot of room.

This experiment could use an additional negative control: Fan with no filter.

There are many possible explanations for the observed data, for example, the air movement through the fan changes the static charge of the smoke particles, causing them to cling to objects in the room. Or, the smoke particles could be binding the plastic blades of the fan. Or, distributing the smoke throughout the room dilutes the smoke concentration at the sensor. For fun, ask your TA for the full list of possible hypotheses!

At this point, we can't say that the HEPA filters are causal. The tape versus no tape experiment produced unexplained and surprising results, which is even more reason to run careful negative controls.

Now, if we could easily label the smoke particles, e.g., using a fluorophore, and measure their distribution after filtering, we'd know exactly where they're going.

I have air purifiers and humidifiers in every room (I'm in horribly dry CO) and I still just live life sniffling and with a dripping scratchy throat no matter what I do. I take antihistamines, NAC (n-acetyl-..... cystine?) helps a lot, mucinex/gauff.

I was hoping my big air purifiers would catch a lot more dog hair than they do.

Have purifiers/humidifiers been a huge change for some of you? I can't prove that I wouldn't be worse right now without them. I love my huge humidifer it lasts about a week keeping a 10-20% humidity townhouse at 65%. But I think I'm expecting too much out of purifiers. Or have other respitory/sinus problems.

Ultrasonic humidifiers (the ones that generate the fog) generate huge amounts of particulate matter to the point I'd argue they are a health hazard and shouldnt even be sold. If you have any ultrasonic humidifiers replace them with evaporative humidifiers.

I actually discovered this independently when I used my air quality monitor to check the humidity in my house after buying a humidifier and saw PM was in the unhealthy range despite having my very large HEPA filter running in the same room. After some googling I discovered why.

https://www.sciencedirect.com/science/article/pii/S016041202... https://www2.purpleair.com/blogs/blog-home/ultrasonic-humidi...

You just need to use distilled/deionized water in ultrasonic humidifiers. You should not be using tap water as that creates hazardous particles, and you'll pretty soon notice dust over everything. They should come with more clear warnings regarding this issue as its severe and not everyone knows. Additionally the systems could have a simple conductivity sensor to stop running if the conductivity (ie. the TDS is too high).

You also need to sterilize them. Frequently. So frequently that you shouldn’t be using them in the first place.

I've never experienced this issue, I assume the symptoms are mold growth or odors?

Or just tiny little potential pathogens being aerosolized very efficiently.

If you take a plastic container and keep it wet for a while, it will grow biofilm.

CO resident here also. I'd recommend stopping everything you're doing except the purifiers and getting a whole house humidifier, because of mold and particulate issues with most portable humidifiers.

Stop the antihistamines because you build a tolerance and they lose their effectiveness - they should really only be taken in one off situations, not regularly(can't actually tell from your post if you regularly take them or just sometime take them).

Air purifiers won't suck up any macro objects like dog hair more than a few inches from them, so you probably want to invest in a vacuum with a built in HEPA filter(i can recommend the dyson gen5 detect, but it is quite pricey)

Also I would check your filters on your HVAC, and get an indoor air quality monitor.

It's also possible you're allergic to something in your house, like mold, or your dog.

I rent so I think I've done all I can. The water here in denver is horrible, I've never lived anywhere with hard water anywhere near this bad where I have to pumice stone lime/calcium off of toilets. I'd 100% have a house water purifier and humidifier if I could. I looked into installing one in a portable manner that I could just bring to places I rent but something about it made me not do it, like a permanent connection or something, I forget.

Only take the antis when I'm bad (maybe for 2 weeks this month, then not for the last 6 months). I've had some respiratory thing going around denver a lot of people are getitng.

My purifiers show indoor air quality and I don't think I've ever seen it not report good. I also just checked the monthly outdoor air on it and that never left good either.

Could be the dogs. Oh well.

If your AQ is not good even with filters, you probably need higher performing ones. Check the CADR rating on them to see if they can handle the space you need filtered.

Your humidity might be too high, 40-50% is recommended for those with allergies.

Get yourself checked for reflux, especially so if it’s worse in the morning.

> I have air purifiers and humidifiers in every room (I'm in horribly dry CO) and I still just live life sniffling and with a dripping scratchy throat no matter what I do. I take antihistamines, NAC (n-acetyl-..... cystine?) helps a lot, mucinex/gauff.

I caught a cold seven years ago and there's been phlegm dripping into the back of my throat ever since.

Medical opinions have been pretty uniformly "sucks to be you, huh? Now go away".

The box fan's CFM is probably a good order of magnitude higher than most commercial purifiers, meaning in theory it should move more air through the filter, thereby cleaning the room faster.

That said, it probably doesn't provide much vacuum/head, so the air that gets drawn through it probably doesn't change much with tape, although I'm guessing the energy draw goes down...

So two comments for DIY air filters, put fiberglass or similar prefilter over the hepa filters, and/or add more filters instead of tape around the fan. Even if they aren't hepa they will catch stuff.

I have a setup like this in my office (but with a larger filter and gaffers tape for the edges). It isn’t smart and it’s loud. I’ve mitigated that slightly by putting it on a wifi plug and running it full blast when I vacuum or when I leave my office for snacks. Seems to work well enough.

Another homemade air purifier post from dynamite. Last update 2021. Posted to HN here:

https://news.ycombinator.com/item?id=28394752

(2021)

Repeat post

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