- 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.
> 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).
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).
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.)
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.
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.
> 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.
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:
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.
> 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)
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.
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.
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.
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.
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.)
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.
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.
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.
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?
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.
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.
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.
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.
- 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.