It was sub $50 a few weeks ago and comes with a Merv 10 filter. You can always buy the heavy duty Lasko 20 x 20 for sub $30 and stick a MERV 13 Filter behind it when it's on. The suction keeps the filter pinned to the back and you get HEPA with VOC removal.
The MERV 13 is neither a HEPA nor VOC filter. It is almost as good as a HEPA filter (it performs the same function albeit it's very slightly less effective), but it doesn't filter out VOCs. For VOCs you need an activated carbon layer.
The Honeywell Ultimate Allergen filter is made of a reinforced pleated media designed to capture particles down to 0.3 microns, 300x smaller than the diameter of a human hair. This filter incorporates the power of Arm and Hammer odor reduction technology into the media in the form of performance enhancing dots. Its large surface area improves the efficiency, providing a greater dust-holding capacity and lower energy costs. The filters electrostatic charge helps attract particles that would otherwise pass through. The Honeywell Ultimate Allergen Filter is effective against the following contaminants: dust/lint, airborne dust mite debris, pollen, pet dander, mold spores, bacteria, microscopic allergens, virus carriers, odor, most smoke and smog particles, as well as VOCs.
Even a MERV 17 will not clear VOCs. You need a chemical reaction, and MERV describes a purely mechanical property.
It is smart to combine an activated-carbon filter with a particulate filter, particularly (heh) if you are operating a 3d printer. Those really foul the air, in ways hard to detect without instruments.
Great study & article. Perhaps incense is not the most scientific test, but it's effective enough for this setup.
Does anyone know if there is raspberry pi add-on or device that acts as an "air quality" sensor, or similar? It would be interesting to monitor this a bit more scientifically in real-time in a variety of environments.
Lastly, I think I've seen this here before, or on reddit. I was inspired to do something similar myself - I use a 19" box fan and a purple 3M MERV furnace filter, 20" square. Except the rounded corners they are almost exactly the same size. Some white duct tape around the edges to seal/hold in place. Total cost is about $40 usd for the fan & filter. I would anticipate a similar performance to the leaky MERV's, as mine is filtering more air as a ratio to total air flowed by the fan.
Yes, just set up a sensor with home assistant (HA). Incredibly easy. Raspberry pi runs the HA server. The air quality sensor is attached to an ESP32 running ESPHome: https://esphome.io/#air-quality
Almost plug and play. Compiles the FW, flashes it, and the device auto connects to the network and is ready for integration into HA. I used the HM3301 air quality sensor FWIW. You can see my filter here: https://news.ycombinator.com/item?id=28395232
Last year when the west coast was blanketed in smoke, I setup a box fan with a HEPA filter. It probably helped, but we also found that the fan's motor was working really hard. The cord's connection point to the fan started melting (unbeknownst to us), causing the fan to intermittently cut out. I only noticed the problem when, long after the forest fires were gone, we noticed a strong smell of melted plastic coming from the fan itself.
All in all, probably a good tradeoff to clean our air during the dangerous smoke levels, but there's the risk of burning out the motor.
You just need to increase the total area of the filter material that the fan is pushing air through. I've seen people shape them into a triangle or box with plastic/tape over seams or openings.
Do we know how the air flow improves in proportion to surface area? I assume it's not quite linear. It would be good to know whether it's worth the effort to do what you're describing.
I'm sure there is an answer to that but this is DIY, so maybe just touch the fan while its been operating for a while, say "damn that sucker's getting hot!" and add more surface area until satisfied you won't burn your house down.
That's because box fan are not designed as static pressure fan. They are a airflow fan for the purpose of moving much air as possible with minimal resistance. Static pressure designed as forced pull/push air, it have slightly thick blade and have a different motor for it. The air purifier uses the static pressure fan because of the filter media.
Take computer fans for example. There are two common case fan type, the airflow and the static pressure. The airflow fan is for the tower case, the static pressure one is for the radiator (water-cooling kit).
Try putting the filter on the suction side of the fan. This will put less load than normal on the fan and there should still be enough airflow to cool the motor.
Technically, since you're sending the air through the filter multiple times, you don't need a HEPA filter. HEPA filters are optimized for single-pass airflows.
And there are thicker filters which give you more pleats, and thus less air impedance, in addition to the "triangle" method suggested by a sibling comment.
If you notice your fan motor or cord getting hot you can reduce the pressure differential (and therefore torque/load on the motor) by allowing some airflow to get around the filter- i.e. push the filter a bit to the side or add a tiny gap between the filter and the fan by sticking in a little block of wood.
This will come at a cost of filtration effectiveness (less airflow going through the filter) but will save your fan in the long run. Make sure not to let your gap or hole get too big or your filter will stop flowing enough air to work.
The ~$25 box fan I got for a DIY air filter was simply failing to push much air through the 3M filter, but I didn't think to check whether the cord/plug or motor was getting hot in addition.
One thing I've found trying to find HEPA filters is that many reviews complain of the filters themselves having some kind of stinky off-gassing. I don't know what the reason for this is, or if it's a problem, but it is worrying.
Reviews on most air purifiers seem to have examples of exploding fans and melting components almost burning houses down.
It really seems like there's room in the air purification market for a company that is really trustworthy, effective, and affordable. Apple could do it, for example.
I'm pretty happy with my Coway air purifier, and that seems like the consensus based on the reviews I've read. The purifier was pretty affordable, as are the filters (keep in mind that filter costs and electricity consumption can impact cost of ownership much more than the original purchase price!).
> Reviews on most air purifiers seem to have examples of exploding fans and melting components almost burning houses down.
I've read the reviews on my air purifier. These sorts of problems were prevalent among the negative reviews.
Upon further inspection, the cause of most of these problems was the air purifier being shipped with a shrink-wrapped filter already installed. Unsurprisingly, turning it on without removing the shrink-wrap results a loud and non-working purifier at best - and fire, death, and bedlam at worst.
It would be nice to see this test done with other particulate sizes. I'd wonder how effective this is for smaller particle sizes compared to competitors.
I have one that cost me $30 all in and you can't hear it at all on the lowest setting (but still decent airflow when you put your hand down). Honestly the biggest benefit in my home environment is how much it has killed the fungus gnats living in my plants. I checked the filter after running it for a few weeks and it still looked relatively clean, but probably a thousand dead flies were in the bottom of it too. I have taken other measures against these flies with not much success (vinegar traps, sticky paper, watering from the bottom, mosquito bits designed to kill larvae, I tried everything I could find one the internet to no help).
I have box fan filters, and a small room Honeywell filter. On the lowest settings, they're about the same, on the highest, the box fan is definitely a little louder (but moves a lot more air).
Turn them down when you're in a room with them - best advice I ever read.
Yeah, I think these DIY filter plans are great and I've built them myself, but I switched to commercial purifiers because of the sound. I don't have measurements but the box fan is substantially louder than either the Blue Air 211 or the Levoit Core 200 that I have.
Many, perhaps most things with a "Made in USA" sticker are done with prison labor, particularly if made in Louisiana, Mississippi, or Alabama.
States have contracts with such for-profit prisons requiring they be kept fully "staffed", railroading as many victims as needed not to pay contract penalties. Police departments are generally agreeable about such policies; everyone they arrest makes them look more important.
So, to first order, "Made in USA" implies slave labor.
I built a "four filter fan box" this year when the smoke started rolling in (off MERV 13 filters, I think?), and have also gone about getting the measurement devices to verify that, yes, it really does work! I used a round fan, and a lot of tape to seal things to the fan, though it appears this might not matter as much as I thought. The filter area is sufficient that the fan doesn't really struggle - fan motors burning out from a single filter (as someone else reported) is a well known failure mode, and a good reason not to just strap filters flat to a fan. They rely on the airflow to cool, and it's easy to screw that up.
Air quality (in terms of PM2.5 and PM10, the stuff my testers measure) coming out of the fan is very good - far lower than the room, and the filter will start pulling down air particulates in a room fairly quickly. If the room is around 5ug/m^3 PM2.5, the output from the fan is sub-1, and it moves enough air to do quite a few air exchanges per day. It really does make a difference.
I'm using a couple Temtop meters to measure air quality, and while they're Chinesium, they do seem to work fairly well.
Also, if you ever wondered: Use your stove's vent fans! The air quality difference in PM2.5/PM10 between cooking without those running, vs cooking with them on, is HUGE! I'll see spikes in the kitchen up well past 100ug/m^3 PM2.5 after browning meat, which is worse than it is outside in heavy forest fire smoke!
Filter's airflow restriction is primarily a function of surface area and filtration medium layers. More surface area results in a better airflow and more filtration medium layers results in a worse airflow.
To maximize surface area of a filter, you can get a thicker accordion filter. This will generally provide good airflow and filtration characreristics.
Sorry about video links below, I liked them at chart times, so you don't have to watch the video to check out the summary.
Here is an example of airflow restriction vs filter. Note that 4 inch Honeywell filter only provides small static pressure rise over no filter option: https://youtu.be/RkjRKIRva58?t=456
Thicker filters cost more, but also last longer. General rule seems to be that when you double the filter thickness, time between replacements doubles as well.
It’s more a function of surface area to volume ratio of the filter. More surface area to volume means more energy is lost due to flow friction between the air and filter walls. However the trade-off is that a higher surface area to volume ratio results in higher filtration efficiency so you have to optimize between flow rate and filter efficiency to get a
overall optimum filtration performance.
As part of your testing, did you notice a big difference in the amount of airflow when you attached one versus four filters onto the fan? I wish to know how important that surface area is for air flow.
We saw a huge improvement in air quality (less smoke, less steam, less grease) when I installed a vent to the outside so the microwave fan over the stove could vent outside instead of just circulating the smoke through some charcoal filters.
That makes sense during normal times, but when the air quality outside is hazardous, venting the air outside means it's pulling unfiltered air inside your house. So use sparingly.
The last time I lived in a place with an unvented stovetop microwave fan, the previous owner never bothered to install the filters, so it was just recirculating unfiltered air.
It pull in outside air, yes, but things are more dynamic than that. Most likely you don't have perfect seals on all your windows, walls, doors, pipes, fans etc.
Secondly, the air from cooking is generally very bad, especially if you're using nonstick surfaces or using much of anything with oil. It's probably better to trade it for smokey air outside.
I keep seeing articles about these and I have to ask: are people actually building them? Sure they work but they’re so ugly. Is it really worth saving $40 for your bedroom to look like a garage?
What's better? My bedroom having some home built filtration art in it, or the inside of my lungs looking like they've sucked down a lot of forest fire?
If you care that deeply about what your room looks like, great. There are plenty of good looking air filters you can pay lots of money for. I'll spend far less to have a far better filter out of the deal.
OP's comparison wasn't a homemade filter versus no filter, it was versus commercial options.
I've done box fan filters before, and they certainly help if they're what you can afford or can find in stores, but after enough years of dealing with wildfire smoke this year I invested in commercial units and I am significantly happier.
After doing a fair amount of research, I ended up with a series of Coway units. They're more expensive than box fan filters, but they're smaller and significantly quieter, especially with a sensor-driven auto mode that adjusts fan speed based on detected pollution levels. This means I'm far more willing to leave them on all the time and get the benefits 24/7. The fact that they're multi-stage is a big plus too, particularly with cat hair around. It means that I have to clean the outer charcoal filters more often but the inner HEPA filters only 1-2 times a year. As an added bonus, power consumption is significantly lower than my box fans.
Which Cowan units do you use? The only concern I have with smaller air filter devices is they sometimes can have significantly less surface area than the furnace filters typically used with box fans.
The Airmega 400 for the main living room and a pair of AW-1512/Airmega 200 (they're the exact same unit with cosmetic differences, get whichever you can find in stock unless you strongly prefer the look of one). Surface area wasn't my main focus. I'd rather change filters more often (not that that's a huge issue outside of wildfire season) and deal with a quieter unit.
These articles made sense 5 years ago when there were only a few high priced air filters widely available online, but now the chinese copies have proliferated amazon and other sites and the market is pretty saturated imo. My filter was $30, about the size and look of a larger bluetooth speaker, it is dead silent on the lowest setting, replacement filters another $15 or so, and its good to filter my bedroom pretty heavily in terms of square footage. Can't beat that. At that price we have one of these in a couple different rooms.
Ditto. Mine is really quiet too on low settings, which is great if you want to leave it on while you sleep.
They also have a carbon layer that's supposed to help with odours and that pollution that can't meaningfully be caught by a simple HEPA filter, although I don't know how effective it is.
Have you actually measured particulates to see if it is doing its job? Currently running a box fan plus filter but might switch if these are actually good.
I am using a cheap Xiaomi (there's not much choice where I live), and a few PMS5003 sensors scattered around the apartment. It works fine for 25 m²-something room when it's relatively clean outside (around 100 µg/m³ or less), but you really have to push it (and suffer the resulting noise) when pollution outside goes above 300 µg/m³ or so. It's been able to keep indoor air around 20 µg/m³ with outside levels going above 800 µg/m³, but I have to use ear plugs because the noise is impossible to tolerate for more than half an hour (and it's pretty difficult to sleep next to).
If you let the heavily polluted air in (a few hundred µg/m³), then close the window and set the purifier to maximum power, it cleans the room in ~20-25 minutes.
I have built two. $40 for the both of them (cheap box fans), and a 20x20x1 filter fits the back quite nicely. They look good enough, and they work fantastically.
In one month of north-west smoke, they got nasty as hell, which is that much less crud aggravating my lungs.
I have seen variations of this used to build laboratory flowhoods. People have been building variations of these in amateur bio labs for the past 20 years and probably longer.
There was a particularly nasty American west coast wildfire a couple years ago, skies red like a science fiction movie. Air purifiers were sold out everywhere, but you could still get a box fan and a couple furnace filters.
> but you could still get a box fan and a couple furnace filters.
That wasn't my experience. The day the smoke moved in, I ran to the home store to grab a couple extra furnace filters, and there was a steady stream of people grabbing them, and heading to the box fan section. The secret seems to be out.
Yeah, the filters sold out everywhere here in Washington State in Sept 2020. My daughter was in Yellowstone at the time and, on her drive back, stopped at multiple home and hardware stores along the way and found none available.
Even when you tell yourself that you do not care, it still has an impact on your mental state. I used to have a dump of a room with junk like this stacked up and after getting rid of it all, I just felt so much better while being in the space.
In my experience, no it's not worth it indoors in a relatively clean environment. I built 3 of these for myself with dust, carbon, & hepa filters, and I used them for over a year.
They are louder, use more energy, are less efficient, uglier & cost more money than several store bought alternatives which often include several carbon & hepa filter replacements which is the main expense in building these fans.
They work well in the garage though, and if you don't plan on changing the filters frequently they are the cheapest build option.
> Is it really worth saving $40 for your bedroom to look like a garage?
What is more important to you: superficial nonsense such as looks or your health?
Go ahead and spend the money so your crush pad can retain its splended wonder while the rest of us breath happily along with some extra dough in our pockets.
Or I can just spend $40 more and get a nice looking air purifier? You’re making a false dichotomy. That’s like asking if I would rather wear plastic bags or be naked. There’s other options
The custom purifiers always have proprietary filters. That’s where they make their money. It isn’t $40 difference, it’s $40 per year. Often more. And once they stop selling that model, they’ll discontinue the filters and so you’re buying another one. And another. And another. Each with its own problems that you have to live with or shop around for, which means more purifiers purchased while sorting it out.
To each their own, but I agree, I like having a tidy living space and an ugly box fan contraption isn't too high on my list, just to save a few bucks.
Even then, I just keep a big stack of furnace filters handy and swap them regularly. When we got hit with the wildfire smoke last year I put in a new filter every day. More practical than putting box fans around the house.
Now that regular cost-effective home HEPA filters are widely available I mostly rely on those. However, I find that the box fan + furnace filter works really well in the window to bring in fresh air without letting the pm2.5 in. This is nice because otherwise CO2 levels build up and it gets stuffy inside. This works on all but the worst days when you can really smell the fire/smoke outside, AQI > 200.
Overall, its not the prettiest and I'd prefer a HEPA filtered energy recovery ventilation but I'm not going to install that in my rental for a couple weeks a year. Usually in Oakland climate the windows are open.
- 20x20x4 MERV12 filter. The 4-inch pleating is key here, to reduce the air resistance on the box fan.
- 1 inch dust pre-filter. This is course, low air resistance, and is for increasing the life of the more expensive MERV12/HEPA filter (so it doesn't get clogged with easy to filter dust).
- Both filters are on the intake side of the box fan. This means you don't need a bungee cord because the intake has negative pressure, the filters just "stick". It also means you keep your box fan flowing with only cleaned air.
The only thing set up was the raspberry pi having an OS installed. Had never used HA or ESPHome before. I was shocked how easy it was if you're comfortable with a terminal. I'd never even used docker before.
My steps were:
1. Install docker
2. Install/run HA through docker
3. Install/run ESPHome through docker (there's a config wizard)
4. Edit the ESPHome .yaml from (3) to my preferences
5. Connect 4 wires from the ESP32 to the air quality sensor
6. Plug ESP32 USB to RPi
7. Run docker esphome on the above yaml. This compiles, flashes, and boots your ESP32, auto-connecting to your network
8. Add the ESP air quality sensor to HA through the web GUI
That's (almost) exactly what I did and without prior docker experience. I must admin it was less hassle with docker, but still docs for particular containers had to be read to understand configuration options.
+ setting up for external access, letsencrypt and tying that everything within docker-compose. I didn't manage to do it in 20minutes, but more like full working day maybe?
Anyway, HA is recommended. Haven't tried ESPHome, but Tasmota is an alternative that also does the job, if you someone ever wants to research the options.
Turnkey microcontroller projects can be really quick. Adafruit and Sparkfun sell many of their breakout boards with special cables for I2C now, so you might not even have to solder anything. From there, you can drag a Python script to the microcontroller (which appears on your PC as a flash drive).
Building enclosures for these projects used to be an annoyance, but everyone provides CAD models of their stuff now, so you just kind of lay it out in your CAD program, extrude a box around it, and print it out.
Never been a better time than now to be building sensors and that sort of thing. (Even with the STM32 shortage!)
As for the Raspberry Pi -- my rule is to treat embedded systems like hardware. Download a Linux image with the software you want on it, copy it to an SD card, plug that in, and go. I use this model for Octopi and while I might have changed the password and uploaded a profile for my printer file, that's it. If the RPI blows itself up, $35 and 5 minute fix. What version of systemd is running? Don't care. How close is the clock to Coordinated Universal Time? Don't care. It's an appliance and the time on the front is blinking :P
(I spent most of my free time this week unbreaking my Beaglebone that I ostensibly don't treat that way -- I log in and fuck with shit. Though when debugging failed I just blew everything away and copied over what I saved in the project's Git repo. It was enough to be back up and running with no loss of functionality. I guess the key is: don't let it run away from you -- it can be an endless time and energy sink.)
You seem to have relatively clean air already. I probably wouldn't even bother with air purifiers in such a situation.
Where did you buy air filters? I live in a third-world country and couldn't find them anywhere, so I had to buy a factory-built purifier. It really struggles to keep up when it's 1000+ µg/m³ outside. I'd like to add a second one (preferably DIY).
Sure, air quality is relative, but 100 AQI is the point where I start getting headaches. Obviously it can get much worse.
I got the air filters on Amazon, which can be US centric, but usually you would get them at a home/hardware store. They are made for slotting into a furnace/HVAC set up. For places where that is less common, they may be harder to find.
Obviously this is very hard to estimate and you shouldn't trust this as anything more than at most a rough order of magnitude estimate. But it does suggest that the ambient levels they are experiencing are worth reducing if you can do it easily.
It's entirely possible! But my perspective is that there's a very one-sided risk. It's extremely unlikely that particles are beneficial. Thus, given the uncertainty I think it's good decision theory to run a purifier, especially given how easy it is relative to other lifestyle changes that could plausibly have a benefit of the same magnitude.
Running a purifier does cause noise however, which isn't healthy; assuming your purifier is close by. (No idea at what point those two effects are of similar impact.)
> It really struggles to keep up when it's 1000+ µg/m³ outside
Also worth noting that 1000ug/m³ is not accurate, maybe you are thinking of some other measurement? In the literal middle of a forest fire, you may see readings of ~300 ug/m³. No where on earth sees readings of 1000+ µg/m³.
It is very much accurate. This is a pretty typical PM2.5 level at winter time where I live. Put a few thousand houses heated with coal close together, add −30-40 °C winters, a particularly bad location where wind almost never blows (maybe ~30 days per year total), and voila.
I don't think the purple air sensors (laser scattering plantower sensors) are very accurate at such extreme measurements. There are numerous laboratory permanent sensors deployed by various state, federal and local authorities that you can compare. I've seen purple air at much more extreme values. Still terrible.
Well, if you find it hard to believe, I welcome you to visit us and live here for a year or two. Don't forget to bring a good supply of spare lungs.
These measurements are supported by the official (state-sponsored) air quality monitoring.
I am not saying we have 1000+ micrograms 24/7. The daily average in winter time is closer to 300-500, depending on your location. However, I see such extreme measurements pretty much every single evening, with some going above 1500 µg/m³.
Back in the days of the great London smog particulate concentrations were going up to 5 _milli_grams per cubic meter:
Do you live in a place where forced-air heating is common? If so, you should be able to buy filters wherever people go to buy miscellaneous hardware for houses. In the US, they are rated on a scale called MERV. In other countries, other rating systems are used. You want something at or near the high end of the scale — getting near 100% removal with, for example, a real HEPA filter is unnecessary and potentially counterproductive, but getting to at least, say, 30% reduction in fine particles per pass is important. In the US, this is around MERV 13.
> You seem to have relatively clean air already. I probably wouldn't even bother with air purifiers in such a situation.
Everyone should have filters. Filters are for more than dust, they have also been shown to greatly reduce the amount of COVID in the room air. (i would assume flu and other viruses as well). Cheap and easy, with no stupid controversy like masks or a vaccine (even though both are better than an air filter, every little bit helps)
Edit: I'm not anti-mask. I would love it if you explained how ill-fitting cloth in a single pass is better than multi-pass HEPA or equivalent filtration rather than (or even as well as) down-voting, though.
A simple cloth mask doesn't really protect the wearer; it protects others from the wearer. It slows droplets down as you exhale them. So they travel X feet, instead of X+Y feet. Depending on air currents and other variables the level of protection this offers others will range from "nothing at all" to "some".
Obviously, a HEPA filter is orders of magnitude better. But, is there a HEPA filter directly between you and the person next to you in line at the supermarket?
> A simple cloth mask doesn't really protect the wearer; it protects others from the wearer.
Sure. I'd call that 'different' rather than 'better', but I suppose it's subjective.
> Obviously, a HEPA filter is orders of magnitude better.
You would think, and yet my comment saying so, objecting to 'masks are better than an air filter' (when qualified to ill-fitting cloth as worn by most) is apparently highly objectionable.
> But, is there a HEPA filter directly between you and the person next to you in line at the supermarket?
Not a comparison I made, but yeah, if I went to a supermarket (I'm not, because I almost entirely had groceries delivered pre-pandemic, so now easily enough entirely) I would wear an FFP3 dust mask rather than ill-fitting cloth, which is two nines to HEPA's 3.5.
(More than that is probably not justified since fit won't be perfect, some leakage. Industrially etc. where there's a need for greater filtration I expect that's when you have to step up to fully enclosed hoods. I digress..)
> if I went to a supermarket [...] I would wear an FFP3 dust mask
rather than ill-fitting cloth, which is two nines to HEPA's 3.5.
Good. That would be very safe. Ideally everybody would do that. I'll let you think about how feasible that is.
I mean, your entire argument seems to be that cloth masks aren't perfect, I guess?
They sure aren't. But that's not the claim anybody is making. The evidence-backed claim is that they are better than nothing -- and "doing absolutely nothing" is apparently the hill that hundreds of millions of Americans have chosen to (literally) die upon We are trying to take a step forward from that, via a simple harm-reduction method that almost anybody can afford.
Let me ask you something. How effective would a public health measure need to be before you'd endorse it?
1%? 10%? 99%? 100%?
There have been 40 million confirmed cases in America, and likely several times that amount in reality. Over half a million deaths. Each single percentage point improvement in prevention represents > 400,000K cases and > 6,000 deaths.
I live in an area that had over about 6 weeks with us pm2.5 aqi above 300 almost every day and many days exceeding 400 and it shocks me how many people still don't have filters of any kind and see this kind of DIY fan as excessive and silly. Ok, more filters for me I suppose.
Not sure how this helps. As soon as your kid sneezes near you, you're gonna catch covid. Air quality seems like a solid usage but in your house vs covid/flu? Your fan is gonna lose. Covid from outside your home? It's a non-issue and doesn't happen.
> As soon as your kid sneezes near you, you're gonna catch covid
That isn't for sure. Last I checked (over a year ago, so different variants) 50% of spouses sleeping together didn't catch COVID.
We are reasonably sure that amount of virus particles you are exposed to is a factor on if you will get COVID. So the more you can eliminate the better your odds are.
I haven't been able to prove this well yet but I got the dyson air purifier and it seems to have done really well at reducing my hey fever. Even when leaving home it seems to be not much of an issue. Possibly just reducing the allergens in the air for most of the time makes it not an issue when I experience them outside for short periods.
The pollen comes in through the windows and gets me hard. While I'm at home I have no issues, when I go outside I start to get hit with them but by the time it's really kicking in I'm usually on my way home again anyway.
It's hard to actually prove the air filter did anything since a lot of factors for me have changed since last season but this year I am affected far less than I was last and not feeling any effects right now while some coworkers are.
During fire season this year, living in one of the cities with the worst air quality in Canada this year, I had to double up my fans to keep up when it reaches 400+ US pm2.5 aqi in my home office that is about 300 sq ft. I am using filtrete 1900 20x20x1 from amazon (Canada)
I also have a Dyson air cleaner and it works for moderate to light smoke but it's just not enough for heavy smoke.
You can use two fans, one on intake, one on exhaust. Or three, if you have a particularly fine filter. But building another whole unit to run in another room might be better.
With a #9, one-inch filter, a single fan does fine.
The difference is your "fan/blower" will not function as well as a "compressor".
You want to vent towards the largest, least constrained volume available, from higher constraints towards lower constraints.
> Both filters are on the intake side of the box fan. This means you don't need a bungee cord because the intake has negative pressure, the filters just "stick"
I agree with putting them on the intake side, but I still want them to stay put when the fan is turned off (with the switch or to move it to another outlet or in a power outage).
After using a purifier for two years pretty much non-stop (close to 24/7) I am pretty certain they don't help with dust at all. That's not why we install them, though.
I've found that tacking 'pdf' onto search queries gets through some of the SEO garbage. For instance I did 'home dust filtration pdf' and found this pdf:
I have a couple of blu air purifiers. They really cut down on the amount of dust in the room. We used to have to dust weekly, in the rooms where we have the purifiers we dust maybe every other month now and you can't tell a difference.
Since this describes such a different experience from my sibling comment, I'll have to add that my purifier cleans particulates just fine (close to 0 µg/m³ in summer and 20-40 µg/m³ in winter), which is supported by three separate PMS5003 and a couple of years of data piped into Grafana.
I don't know why it's so useless against dust. Maybe we have more coarse-grained dust which quickly falls down on the ground.
The blu air filter has a prefilter specifically for dust and it gets filthy. That has to get washed in the laundry regularly. Maybe some combination of that, it's cfm's and placement might make a difference?
I have 2 coway units in a ~800sqft apartment and still have tons of dust but I open the windows a lot when its not smoky and I have a dog so who knows. The pre-filter does trap a lot of dust so there is obviously some (maybe minor) reduction.
4 inches is deep for a standard dimensioned MERV-rated filter. It’s normal for a high quality but sadly usually proprietary fancy HVAC filter (Aprilaire, Lennox, etc).
That's true, but I want to know what they meant when they said the 4-inch pleating is designed to reduce air resistance. Since it's an unusually large amount of depth for a MERV filter, I would expect the opposite to happen?
Feel the air coming out, vs without a filter. The slower the air is, the fewer opportunities you get to trap each dust grain. Overall miss rate improves exponentially with airflow speed.
You might imagine so, but that turns out not to be how it works. Each time through there is a chance the particle will be blocked. It doesn't matter how fast in went in, because the mv^2 of a dust mote is tiny at any plausible speed. What matters is that N trips through gives you (1-p)^N probability of not getting caught, which falls off very fast... in fact, exponentially.
A deeper-pleated filter is the way to reduce velocity in traversal.
I've used both. I don't have hard numbers since they are different filters, but I replaced a 1" filter with a 4" filter and I can run my fan at a lower speed.
The 4-inch pleating translates into a larger surface area of filter material, which in turn means the flow rate per area is reduced. So you have the same amount of air going through 4x the area of filter material compared to a 1" filter. Its analogous to using a thicker wire with the same current.
Nice setup! Could you also share the names (brands/model, e.g. 3M Filtrete 20x20x4) of the three components? I see a few options out there but rather go with something that is vouched for here.
> This was unexpected. I thought the tape would help, but I wouldn’t have been surprised if it hurt instead. Instead, there’s basically no difference at all. I don’t know enough about fluid dynamics to even speculate about what’s happening here, so I won’t try.
The fan pumps as much air through the filters as it will, regardless of whether the areas not covered by fans are taped off or not.
I have one "built" in my house right now. I say "built" as I have simply bungie-tied an air filter to a box fan. I have also hooked it up to one of those analog outlet timers so it's not running the whole day. I'm sure folks on HN could do a much better and more interesting job:
- Rasberry Pi Zero runs PM2.5 sensor.
- Fan is controlled by Raspberry Pi Zero.
- Fan only turns on when PM2.5 levels are over threshold for n seconds.
- Fan only turns off when PM2.5 levels are below threshold for n seconds.
- Add some collection and graphing of PM2.5 levels over time for fun.
Oh, ha! So much for my reading comprehension.
Thanks for the link. I think that should be compatible with a Pi. I can try it out in a couple weeks when I get some free time to tinker.
I have a PM2.5 sensor hooked to a Raspberry Pi Zero W, I use the PMS5003 ($40 at Adafruit). I have a script running in a screen session that posts its measurements once a minute to a Google Cloud Function which then inserts it into BigQuery, and then a DataStudio dashboard to visualize the data.
The cloud cost is $0, it all falls in the free tier. The Raspberry Pi Zero W is just $10.
I have a separate station with an SCD-41 CO2 sensor (+ temp/humidity/pressure with an MCP9808) all hooked up to a TinyPico board with Stemma QT that also post metrics to BigQuery in a similar way. And yes I'm planning to combine both into a single device very soon :-)
Wonder if any PC gaming case manufacturers will ever think to add some HEPA filters to the unit - be good for the PC to have cleaner air going in and that airflow out would be put to good use to cool the PC.
I recall seeing a video (BigClive on YT) in which he gets a fan and used a peace of kitchen roll as a filter and found it fairly effective and just dug that out - https://youtu.be/kK7sJq2E0bE
But then you’d have to change the filters and if you didn’t possibly cause airflow problems and then overheating. It would be a nice feature as long as you keep up with it though.
Probably cheaper MERV 8 filter would make more sense, since for this application you're mostly concerned about those larger dust particles. Also it seems like this would be a job for the fan manufacturers rather than the PC case manufacturers. The fan just needs a little slot where you can slide in a thin replaceable filter.
you don't really want something that extreme for case fan intake. you end up "paying" for the cleaner air with higher temps or faster (louder) fans.
there are some newer cases with a fine mesh screen over the intake fans. I have these in my fractal meshify 2, and they seem to work pretty well so far.
I used to have a PC case with a cooling fan filter -- by the time I retired that PC, the dust was nearly an inch thick. I had forgotten that it had a filter, and "out of sight, out of mind". It wasn't even a HEPA filter, just a fine mesh.
I upgraded my heat pump and furnace system last year and spent the extra money to put in a filtration system. We had a two week stretch with AQI of 500+ outside from the fires and never even got a hint of smoke in the house. Great investment.
I've made one of these, and they do work extremely well, but they're missing one key thing that I now consider vital: Activated Carbon.
A HEPA filter is doing the heavy lifting within any air purifier, it is therefore the most important ingredient. Activated Carbon is well known for removing smells/cents, but it does more than just that: It also neutralizes VOCs and some other gaseous pollutants which can travel through a HEPA filter.
This is why I currently have a commercial air filtering solution instead of my box fan + 3M filter, it has suspended Activated Carbon around the HEPA filter fabric. I don't know how I'd achieve that with my box fan solution, and I've not seen anyone else try to address it.
Other air purification technologies have safety issues (e.g. ionizers, ozone) or just outright don't work (e.g. UV light inside a channel). HEPA and Activated Carbon have measurable upsides with no downsides aside from their cost. They're the best we have today in spaces occupied by people.
A DIY solution would be to get activated carbon that's intended for water filtration (fish tanks, etc). Then add a step that moves the air through the media (put it into a mesh box, or heck even just blow the air down onto the carbon that's sitting in a "dish" or some kind.
Certainly not as efficient as a commercial all-in-one solution, but it that's not available to you, it can work.
You can even make your own "activated charcoal" but it's a pretty messy and time consuming process.
Would activated charcoal for aquarium work thought for gas? We're talking about a significant difference in porosity here. Even going with something like ROX (https://www.bulkreefsupply.com/bulk-premium-rox-0-8-aquarium...) it's going to have much larger pores and much smaller surface area than a carbon coating on a filter
Good question. I'm imagining that with a small enough space / large enough quantity of charcoal you'd still get benefits, but it's not like I sat down and tried to do all the math.
Yeah the activated carbon filter in my commercial purifier is just a sheet that sits in front of the filter. You can buy one and duct tape it to the DIY solution. It has to be vacuumed regularly and eventually replaced.
Also there doesn't seem to be any need to worry about sealing the filters as the author's experiments showed, and because the stuff you're filtering is already floating around. It would matter in a vacuum cleaner or some such pollutant-kicking stream.
I had considered something similar, but recently I found that Ikea has started selling air purifiers and sensors for very reasonable money.
They even sell an activated carbon filter that you can add.
For years I had planned to make a DIY one, but never got round to it. But a week ago bought one of the IKEA ones, plus a carbon filter, and I've been very happy. The air feels cleaner and somehow just nicer.
Lots of reviews say it's underpowered for a normal sized room compared to alternative products. But for me, the alternative is a DIY one that I still wouldn't have got round to making.
I've been running one of these for a few months. The filter has slowly turned darker brown - which suggests it's working (not anywhere near forest fires here!).
It has a trickle mode which is completely silent and uses about 1W of power. Something you won't get on a DIY fan.
This is awesome. I love DIY stuff and love the idea of an affordable clean air solution. For me, the aesthetics, noise, and issues like overworking the fan motor, make the extra $50 for a purpose-built filter worth it.
For the one I purchased, I researched them on Consumer Reports, which independently assessed their efficacy. How do you tell they work less well before you make that assertion?
I've built a few of these and compared with higher end air purifiers like Alen. The only downside I could find with the DIY box fans was the power consumption is much higher.. about 60W vs 6W for the commercial purifier.
That is a $30/yr increased cost in electricity based on CA rates.
It's about power efficiency, not total power draw. Use less powerful fans with an inefficient setup and you're not cleaning your air as well. Engineers put thought into chassis design and motor/fan specs.
For this same reason I decided to get a used box from a reputable, long lasting company with top of the line CADR, and I can find plenty of aftermarket HEPA filters that are compatible.
That was a comparison was roughly for the same air cleaning rate. I think it has to do with the fan architecture. With purpose built purifiers using static pressure fans instead of air fans.
Wirecutter performed a similar experiment a few years back. Their results were somewhat different, showing that the DIY version helped significantly, but not nearly as well as the best of the commerical ones they tested:
The wirecutter DIY test used a filter with a rating of FPR 9. Since FPR isn't standardized like MERV or HEPA, it's hard to tell what this means, but likely to be < MERV 13. The OP used a HEPA filter on their testing which is > MERV 16.
Yikes. Putting high pressure drop genuine HEPA filters on a fan like that where most of the air will bypass them defeats the purpose and is a waste of energy and money. Just get a bigger MERV 13 or better filter and cover the whole fan.
Based on his testing, it looks like it achieves purpose just fine, and slightly better than the more expensive option.
> and is a waste of energy and money
His setup has over 5 times the filter area (1,400 cm² at 5 cm thick vs. 300 cm² at 4 cm thick), for $10 more on the filter replacement. Energy use is higher, but it's not clear that it exceeds the savings from cheaper filter replacements.
And by having those gaps in the filters, the fan motor is probably being saved from overheating. Plenty of air still gets entrained through the filters, even with some bypass.
It's kind of like premature optimization when writing a program. Where you think improvements are needed isn't necessarily where they should be. Test your code, find the hot spots, and improve those. With a filter setup, it might see obvious that a good seal is needed between filter and fan. Turns out, that's not always true.
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[ 3.1 ms ] story [ 290 ms ] threadhttps://www.amazon.com/Lasko-FF305-20-inch-Purifier-Purifyin...
Here is a substitute.
FPR 12 HomeDepot filter.
https://www.homedepot.com/p/Honeywell-16-x-25-x-1-FPR-12-Air...
The Honeywell Ultimate Allergen filter is made of a reinforced pleated media designed to capture particles down to 0.3 microns, 300x smaller than the diameter of a human hair. This filter incorporates the power of Arm and Hammer odor reduction technology into the media in the form of performance enhancing dots. Its large surface area improves the efficiency, providing a greater dust-holding capacity and lower energy costs. The filters electrostatic charge helps attract particles that would otherwise pass through. The Honeywell Ultimate Allergen Filter is effective against the following contaminants: dust/lint, airborne dust mite debris, pollen, pet dander, mold spores, bacteria, microscopic allergens, virus carriers, odor, most smoke and smog particles, as well as VOCs.
It is smart to combine an activated-carbon filter with a particulate filter, particularly (heh) if you are operating a 3d printer. Those really foul the air, in ways hard to detect without instruments.
Does anyone know if there is raspberry pi add-on or device that acts as an "air quality" sensor, or similar? It would be interesting to monitor this a bit more scientifically in real-time in a variety of environments.
Lastly, I think I've seen this here before, or on reddit. I was inspired to do something similar myself - I use a 19" box fan and a purple 3M MERV furnace filter, 20" square. Except the rounded corners they are almost exactly the same size. Some white duct tape around the edges to seal/hold in place. Total cost is about $40 usd for the fan & filter. I would anticipate a similar performance to the leaky MERV's, as mine is filtering more air as a ratio to total air flowed by the fan.
Almost plug and play. Compiles the FW, flashes it, and the device auto connects to the network and is ready for integration into HA. I used the HM3301 air quality sensor FWIW. You can see my filter here: https://news.ycombinator.com/item?id=28395232
Yes. They contain an annoying tiny fan though that gets irritating fast due to high pitch
All in all, probably a good tradeoff to clean our air during the dangerous smoke levels, but there's the risk of burning out the motor.
Be careful out there.
Take computer fans for example. There are two common case fan type, the airflow and the static pressure. The airflow fan is for the tower case, the static pressure one is for the radiator (water-cooling kit).
And there are thicker filters which give you more pleats, and thus less air impedance, in addition to the "triangle" method suggested by a sibling comment.
This will come at a cost of filtration effectiveness (less airflow going through the filter) but will save your fan in the long run. Make sure not to let your gap or hole get too big or your filter will stop flowing enough air to work.
The ~$25 box fan I got for a DIY air filter was simply failing to push much air through the 3M filter, but I didn't think to check whether the cord/plug or motor was getting hot in addition.
Reviews on most air purifiers seem to have examples of exploding fans and melting components almost burning houses down.
It really seems like there's room in the air purification market for a company that is really trustworthy, effective, and affordable. Apple could do it, for example.
It isn't Apple, but one of their models does have a striking resemblance to an iPod shuffle: https://m.media-amazon.com/images/I/61716qA3rEL.jpg
I've read the reviews on my air purifier. These sorts of problems were prevalent among the negative reviews.
Upon further inspection, the cause of most of these problems was the air purifier being shipped with a shrink-wrapped filter already installed. Unsurprisingly, turning it on without removing the shrink-wrap results a loud and non-working purifier at best - and fire, death, and bedlam at worst.
Turn them down when you're in a room with them - best advice I ever read.
https://dynomight.net/better-DIY-air-purifier.html
My covid project was building a gym in my unfinished basement, and this is the box fan + furnace filter I use to keep the dust levels down.
States have contracts with such for-profit prisons requiring they be kept fully "staffed", railroading as many victims as needed not to pay contract penalties. Police departments are generally agreeable about such policies; everyone they arrest makes them look more important.
So, to first order, "Made in USA" implies slave labor.
The page cited does not mention prison labor.
The California fire crews do make quite heavy use of prison labor, which seems less problematic than corporate use, except for the safety angle.
Air quality (in terms of PM2.5 and PM10, the stuff my testers measure) coming out of the fan is very good - far lower than the room, and the filter will start pulling down air particulates in a room fairly quickly. If the room is around 5ug/m^3 PM2.5, the output from the fan is sub-1, and it moves enough air to do quite a few air exchanges per day. It really does make a difference.
I'm using a couple Temtop meters to measure air quality, and while they're Chinesium, they do seem to work fairly well.
Also, if you ever wondered: Use your stove's vent fans! The air quality difference in PM2.5/PM10 between cooking without those running, vs cooking with them on, is HUGE! I'll see spikes in the kitchen up well past 100ug/m^3 PM2.5 after browning meat, which is worse than it is outside in heavy forest fire smoke!
https://www.sevarg.net/2021/08/28/temtop-air-quality-sensors...
To maximize surface area of a filter, you can get a thicker accordion filter. This will generally provide good airflow and filtration characreristics.
Sorry about video links below, I liked them at chart times, so you don't have to watch the video to check out the summary.
Here is an example of airflow restriction vs filter. Note that 4 inch Honeywell filter only provides small static pressure rise over no filter option: https://youtu.be/RkjRKIRva58?t=456
At the same time, same filter is 5th overall in large particle removal: https://youtu.be/RkjRKIRva58?t=661
Thicker filters cost more, but also last longer. General rule seems to be that when you double the filter thickness, time between replacements doubles as well.
We saw a huge improvement in air quality (less smoke, less steam, less grease) when I installed a vent to the outside so the microwave fan over the stove could vent outside instead of just circulating the smoke through some charcoal filters.
The last time I lived in a place with an unvented stovetop microwave fan, the previous owner never bothered to install the filters, so it was just recirculating unfiltered air.
Secondly, the air from cooking is generally very bad, especially if you're using nonstick surfaces or using much of anything with oil. It's probably better to trade it for smokey air outside.
What's better? My bedroom having some home built filtration art in it, or the inside of my lungs looking like they've sucked down a lot of forest fire?
If you care that deeply about what your room looks like, great. There are plenty of good looking air filters you can pay lots of money for. I'll spend far less to have a far better filter out of the deal.
I've done box fan filters before, and they certainly help if they're what you can afford or can find in stores, but after enough years of dealing with wildfire smoke this year I invested in commercial units and I am significantly happier.
After doing a fair amount of research, I ended up with a series of Coway units. They're more expensive than box fan filters, but they're smaller and significantly quieter, especially with a sensor-driven auto mode that adjusts fan speed based on detected pollution levels. This means I'm far more willing to leave them on all the time and get the benefits 24/7. The fact that they're multi-stage is a big plus too, particularly with cat hair around. It means that I have to clean the outer charcoal filters more often but the inner HEPA filters only 1-2 times a year. As an added bonus, power consumption is significantly lower than my box fans.
They also have a carbon layer that's supposed to help with odours and that pollution that can't meaningfully be caught by a simple HEPA filter, although I don't know how effective it is.
If you let the heavily polluted air in (a few hundred µg/m³), then close the window and set the purifier to maximum power, it cleans the room in ~20-25 minutes.
In one month of north-west smoke, they got nasty as hell, which is that much less crud aggravating my lungs.
That wasn't my experience. The day the smoke moved in, I ran to the home store to grab a couple extra furnace filters, and there was a steady stream of people grabbing them, and heading to the box fan section. The secret seems to be out.
They are louder, use more energy, are less efficient, uglier & cost more money than several store bought alternatives which often include several carbon & hepa filter replacements which is the main expense in building these fans.
They work well in the garage though, and if you don't plan on changing the filters frequently they are the cheapest build option.
It was a stop gap until I could actually get my hands on a large commercial air purifier, those were unavailable at the time.
What is more important to you: superficial nonsense such as looks or your health?
Go ahead and spend the money so your crush pad can retain its splended wonder while the rest of us breath happily along with some extra dough in our pockets.
Then YOU go ahead and do that. My point of arguing your elitist criticism is that some people either don't have or need that extra $40.
The custom purifiers always have proprietary filters. That’s where they make their money. It isn’t $40 difference, it’s $40 per year. Often more. And once they stop selling that model, they’ll discontinue the filters and so you’re buying another one. And another. And another. Each with its own problems that you have to live with or shop around for, which means more purifiers purchased while sorting it out.
Even then, I just keep a big stack of furnace filters handy and swap them regularly. When we got hit with the wildfire smoke last year I put in a new filter every day. More practical than putting box fans around the house.
However, The box fan setup uses a much larger filter and pushes way more air. I only take it out if the outdoor quality is abnormally poor.
Yes it’s ugly and noisy but it’s for emergencies.
Also, you’re saving way more than $40. Wirecutter’s recommended one costs $200.
Overall, its not the prettiest and I'd prefer a HEPA filtered energy recovery ventilation but I'm not going to install that in my rental for a couple weeks a year. Usually in Oakland climate the windows are open.
- 20 inch box fan
- 20x20x4 MERV12 filter. The 4-inch pleating is key here, to reduce the air resistance on the box fan.
- 1 inch dust pre-filter. This is course, low air resistance, and is for increasing the life of the more expensive MERV12/HEPA filter (so it doesn't get clogged with easy to filter dust).
- Both filters are on the intake side of the box fan. This means you don't need a bungee cord because the intake has negative pressure, the filters just "stick". It also means you keep your box fan flowing with only cleaned air.
Heres a pic of my setup: https://imgur.com/a/O4I6Udx
And here's a graph this morning from my air quality sensor, after turning on the fan/filter: https://imgur.com/a/c5GMNcC
The peak at ~30ug/m^3 PM2.5 is approximately 100 AQI. The fan was on the other side of my 900 sqft house from the sensor.
Attached over I2C to an ESP32 running ESPHome: https://esphome.io/#air-quality Which in turn reports to a raspberry pi running Home Assistant: https://www.home-assistant.io/installation/ Took about 20 mins to set everything up.
Given you have Home Assistant installed and have previously used ESPHome. And attached wires.
Otherwise, you may be up to a journey that takes many hours/days. That's the difference experience makes :)
My steps were:
1. Install docker
2. Install/run HA through docker
3. Install/run ESPHome through docker (there's a config wizard)
4. Edit the ESPHome .yaml from (3) to my preferences
5. Connect 4 wires from the ESP32 to the air quality sensor
6. Plug ESP32 USB to RPi
7. Run docker esphome on the above yaml. This compiles, flashes, and boots your ESP32, auto-connecting to your network
8. Add the ESP air quality sensor to HA through the web GUI
+ setting up for external access, letsencrypt and tying that everything within docker-compose. I didn't manage to do it in 20minutes, but more like full working day maybe?
Anyway, HA is recommended. Haven't tried ESPHome, but Tasmota is an alternative that also does the job, if you someone ever wants to research the options.
Building enclosures for these projects used to be an annoyance, but everyone provides CAD models of their stuff now, so you just kind of lay it out in your CAD program, extrude a box around it, and print it out.
Never been a better time than now to be building sensors and that sort of thing. (Even with the STM32 shortage!)
As for the Raspberry Pi -- my rule is to treat embedded systems like hardware. Download a Linux image with the software you want on it, copy it to an SD card, plug that in, and go. I use this model for Octopi and while I might have changed the password and uploaded a profile for my printer file, that's it. If the RPI blows itself up, $35 and 5 minute fix. What version of systemd is running? Don't care. How close is the clock to Coordinated Universal Time? Don't care. It's an appliance and the time on the front is blinking :P
(I spent most of my free time this week unbreaking my Beaglebone that I ostensibly don't treat that way -- I log in and fuck with shit. Though when debugging failed I just blew everything away and copied over what I saved in the project's Git repo. It was enough to be back up and running with no loss of functionality. I guess the key is: don't let it run away from you -- it can be an endless time and energy sink.)
Where did you buy air filters? I live in a third-world country and couldn't find them anywhere, so I had to buy a factory-built purifier. It really struggles to keep up when it's 1000+ µg/m³ outside. I'd like to add a second one (preferably DIY).
I got the air filters on Amazon, which can be US centric, but usually you would get them at a home/hardware store. They are made for slotting into a furnace/HVAC set up. For places where that is less common, they may be harder to find.
By my estimates, a lifelong exposure to 33 µg/m³ rather than 0 µg/m³ would on average result in a loss of around 1 disability adjusted life year.
https://dynomight.net/air/#a-heuristic-to-quantify-harms
Obviously this is very hard to estimate and you shouldn't trust this as anything more than at most a rough order of magnitude estimate. But it does suggest that the ambient levels they are experiencing are worth reducing if you can do it easily.
Also worth noting that 1000ug/m³ is not accurate, maybe you are thinking of some other measurement? In the literal middle of a forest fire, you may see readings of ~300 ug/m³. No where on earth sees readings of 1000+ µg/m³.
The highest purple air sensor, near/on the fire front, in raw PM2.5 ug/m³ is at 368 when I checked: https://www.purpleair.com/map?opt=1/mPM25/a10/cC0&select=735...
These measurements are supported by the official (state-sponsored) air quality monitoring.
I am not saying we have 1000+ micrograms 24/7. The daily average in winter time is closer to 300-500, depending on your location. However, I see such extreme measurements pretty much every single evening, with some going above 1500 µg/m³.
Back in the days of the great London smog particulate concentrations were going up to 5 _milli_grams per cubic meter:
https://sci-hub.se/https://pubmed.ncbi.nlm.nih.gov/29596258/...
It's not impossible or even particularly unusual.
Everyone should have filters. Filters are for more than dust, they have also been shown to greatly reduce the amount of COVID in the room air. (i would assume flu and other viruses as well). Cheap and easy, with no stupid controversy like masks or a vaccine (even though both are better than an air filter, every little bit helps)
Edit: I'm not anti-mask. I would love it if you explained how ill-fitting cloth in a single pass is better than multi-pass HEPA or equivalent filtration rather than (or even as well as) down-voting, though.
A simple cloth mask doesn't really protect the wearer; it protects others from the wearer. It slows droplets down as you exhale them. So they travel X feet, instead of X+Y feet. Depending on air currents and other variables the level of protection this offers others will range from "nothing at all" to "some".
Obviously, a HEPA filter is orders of magnitude better. But, is there a HEPA filter directly between you and the person next to you in line at the supermarket?
Sure. I'd call that 'different' rather than 'better', but I suppose it's subjective.
> Obviously, a HEPA filter is orders of magnitude better.
You would think, and yet my comment saying so, objecting to 'masks are better than an air filter' (when qualified to ill-fitting cloth as worn by most) is apparently highly objectionable.
> But, is there a HEPA filter directly between you and the person next to you in line at the supermarket?
Not a comparison I made, but yeah, if I went to a supermarket (I'm not, because I almost entirely had groceries delivered pre-pandemic, so now easily enough entirely) I would wear an FFP3 dust mask rather than ill-fitting cloth, which is two nines to HEPA's 3.5.
(More than that is probably not justified since fit won't be perfect, some leakage. Industrially etc. where there's a need for greater filtration I expect that's when you have to step up to fully enclosed hoods. I digress..)
I mean, your entire argument seems to be that cloth masks aren't perfect, I guess?
They sure aren't. But that's not the claim anybody is making. The evidence-backed claim is that they are better than nothing -- and "doing absolutely nothing" is apparently the hill that hundreds of millions of Americans have chosen to (literally) die upon We are trying to take a step forward from that, via a simple harm-reduction method that almost anybody can afford.
Let me ask you something. How effective would a public health measure need to be before you'd endorse it?
1%? 10%? 99%? 100%?
There have been 40 million confirmed cases in America, and likely several times that amount in reality. Over half a million deaths. Each single percentage point improvement in prevention represents > 400,000K cases and > 6,000 deaths.
That isn't for sure. Last I checked (over a year ago, so different variants) 50% of spouses sleeping together didn't catch COVID.
We are reasonably sure that amount of virus particles you are exposed to is a factor on if you will get COVID. So the more you can eliminate the better your odds are.
It's hard to actually prove the air filter did anything since a lot of factors for me have changed since last season but this year I am affected far less than I was last and not feeling any effects right now while some coworkers are.
I also have a Dyson air cleaner and it works for moderate to light smoke but it's just not enough for heavy smoke.
I've also heard airflow dynamics arguments, but I feel like I've heard them argued in both directions.
With a #9, one-inch filter, a single fan does fine.
Intake still allows the air coming out to be more turbulent, mixing with the existing air better and giving it more "throw" in larger spaces.
https://www.youtube.com/watch?v=zE4qmN_EOXw
edit1: exact time of the result https://youtu.be/zE4qmN_EOXw?t=250
I agree with putting them on the intake side, but I still want them to stay put when the fan is turned off (with the switch or to move it to another outlet or in a power outage).
How can you even search for this? Google results are not relevant to dust at all:
https://www.google.com/search?q=diy+air+dust+filter
This is a really strong example of how bad goog sucks for long-tail queries.
SEO spammed: https://www.google.com/search?q=home+dust+filtration+old+hou...
https://www.epa.gov/sites/default/files/2018-07/documents/re...
which cites this paper about deposition rates of different particle sizes:
https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=86094...
Try this: https://www.google.com/search?q=diy+air+%22dust+filter%22
I don't know why it's so useless against dust. Maybe we have more coarse-grained dust which quickly falls down on the ground.
Also, 4 inches is quite a lot of depth for a MERV filter, could you elaborate on this point?
A deeper-pleated filter is the way to reduce velocity in traversal.
I know its working because I don't smell smoke, but I'm curious to see a measurement
Warning: The fan motor gets cooled from the airflow. This is drastically altered to something it is not designed for, and can result in fire.
The fan pumps as much air through the filters as it will, regardless of whether the areas not covered by fans are taped off or not.
- Rasberry Pi Zero runs PM2.5 sensor.
- Fan is controlled by Raspberry Pi Zero.
- Fan only turns on when PM2.5 levels are over threshold for n seconds.
- Fan only turns off when PM2.5 levels are below threshold for n seconds.
- Add some collection and graphing of PM2.5 levels over time for fun.
Previously, I had sensor from this family hooked up to a Raspberry pi doing measurement only:
https://www.amazon.com/AITRIP-Precision-Quality-Detection-Co...
The cloud cost is $0, it all falls in the free tier. The Raspberry Pi Zero W is just $10.
I have a separate station with an SCD-41 CO2 sensor (+ temp/humidity/pressure with an MCP9808) all hooked up to a TinyPico board with Stemma QT that also post metrics to BigQuery in a similar way. And yes I'm planning to combine both into a single device very soon :-)
I recall seeing a video (BigClive on YT) in which he gets a fan and used a peace of kitchen roll as a filter and found it fairly effective and just dug that out - https://youtu.be/kK7sJq2E0bE
there are some newer cases with a fine mesh screen over the intake fans. I have these in my fractal meshify 2, and they seem to work pretty well so far.
A HEPA filter is doing the heavy lifting within any air purifier, it is therefore the most important ingredient. Activated Carbon is well known for removing smells/cents, but it does more than just that: It also neutralizes VOCs and some other gaseous pollutants which can travel through a HEPA filter.
This is why I currently have a commercial air filtering solution instead of my box fan + 3M filter, it has suspended Activated Carbon around the HEPA filter fabric. I don't know how I'd achieve that with my box fan solution, and I've not seen anyone else try to address it.
Other air purification technologies have safety issues (e.g. ionizers, ozone) or just outright don't work (e.g. UV light inside a channel). HEPA and Activated Carbon have measurable upsides with no downsides aside from their cost. They're the best we have today in spaces occupied by people.
Certainly not as efficient as a commercial all-in-one solution, but it that's not available to you, it can work.
You can even make your own "activated charcoal" but it's a pretty messy and time consuming process.
Also there doesn't seem to be any need to worry about sealing the filters as the author's experiments showed, and because the stuff you're filtering is already floating around. It would matter in a vacuum cleaner or some such pollutant-kicking stream.
Ikea FÖRNUFTIG: https://www.ikea.com/us/en/p/foernuftig-air-purifier-white-5...
Lots of reviews say it's underpowered for a normal sized room compared to alternative products. But for me, the alternative is a DIY one that I still wouldn't have got round to making.
I'd recommend it.
It has a trickle mode which is completely silent and uses about 1W of power. Something you won't get on a DIY fan.
Could you confirm the technical spec of the filters you are using? Actual rating? Is it actually HEPA?
The ikea website seems to just be pretty vague marketing stuff with no details.
[0] https://www.wired.com/story/ikea-fornuftig-air-purifier/
> The particle filter is tested according to EN 1822-1 and ISO 29463-3 which corresponds to class EPA12.
But many "purpose-built" units just cost more, but work less well. How do you tell if it will work well, before you spend?
That is a $30/yr increased cost in electricity based on CA rates.
For this same reason I decided to get a used box from a reputable, long lasting company with top of the line CADR, and I can find plenty of aftermarket HEPA filters that are compatible.
https://www.nytimes.com/wirecutter/reviews/best-air-purifier...
I wonder what accounts for the difference in results.
Ben Kuhn and Dan Luu have written about this, Cf.
Based on his testing, it looks like it achieves purpose just fine, and slightly better than the more expensive option.
> and is a waste of energy and money
His setup has over 5 times the filter area (1,400 cm² at 5 cm thick vs. 300 cm² at 4 cm thick), for $10 more on the filter replacement. Energy use is higher, but it's not clear that it exceeds the savings from cheaper filter replacements.
And by having those gaps in the filters, the fan motor is probably being saved from overheating. Plenty of air still gets entrained through the filters, even with some bypass.
It's kind of like premature optimization when writing a program. Where you think improvements are needed isn't necessarily where they should be. Test your code, find the hot spots, and improve those. With a filter setup, it might see obvious that a good seal is needed between filter and fan. Turns out, that's not always true.