Double blind studies are helpful when we do not understand they underlying dynamics of a complicated system (like a body) but we want to learn what effect a change has on that system (like a medicine).
If we know pathogens cause disease, and we know filtering removes pathogens from the air (and we can test and verify that) we don't need to run a double blind study to verify they work.
It's the same reason you don't need to run a double blind study on whether seat belts work. We understand the cause and effect of car ejections and windshield/steering wheel impacts on human bodies. Seat belts are designed to mitigate these incidents and are tested and validated in the lab using formal science and engineering.
> It's the same reason you don't need to run a double blind study on whether seat belts work.
We might need some historical investigation into the road that was travelled to get seatbelts to where they are now (physically, legally, and socially). I'm a millennial and I remember growing up where similar arguments were made:
- "If it's my time to go, then it's God's will"
- "It's uncomfortable"
- zero/inconsistent law enforcement
- "If the car rolls over than it can trap you"
To now, where it's entirely automatic and incredibly wild to even suggest being without a seatbelt.
Don't forget the one about how it's safer to be thrown free of a wreck (which will happen if you don't wear your seatbelt) than remain in the car. <sigh>
Its crazy, I was born in the early 80s and I never wore a seatbelt until I started driving. As a kid I would ride in a van that didn't even have seats and think absolutely nothing of it.
I was born in the early 70s and we always wore seatbelts, for as long as I can remember. Though we did routinely ride in the back of the pickup, which isn't something I see happening much today.
You're not going to spend 100% of your day in the coverage of one of these things, so what's the dose response? How many hours per day of filtered air equals how many fewer infections per year? Does air filtration in your workplace matter at all if you have young kids in school? Does air filtration in a school matter at all if the kids are all together on a poorly ventilated bus for two hours a day?
Yes we have studied actual rates of infection in response to interventions like air filtering, so these studies account for all that real-world complexity and messiness you worry about.
The article is complaining that every study doesn't redo the evidence collection, end-to-end, every time. That's not realistic and not necessary.
A lot of your specific questions are leading (with a nothing-we-can-do attitude underneath) or asking the wrong question (eg expecting one universal number for "hours of filtration per infection prevented").
For instance the correct answer may be air filters in classrooms and buses and workplaces, but strangely your line of questioning doesn't even consider that possibility.
This would be like someone in the 1800s questioning how handwashing avoids Cholera if they don't wash their hands at home. I think I see a solution to this one...
> It's the same reason you don't need to run a double blind study on whether seat belts work
Actually, seat belts are a weird example. After they were invented, there were more car crashes since people trusted they were protected. Without seat belts people were more cautious. They were a net positive of course, but some different situations/inventions/studies might have effects that are the opposite of what you would expect.
I support more research but anecdotally HEPA air filters changed my life. I used to get pretty bad respiratory infections every winter but after getting these that went away. I’m talking the simple kind with basic charcoal prefilter and fiber HEPA filter which are about $150 at most home stores or big box stores. Never used any ionization or ozone. The interesting bit is the newer ones even measure air particulates and have a variable speed option where they will speed up when they detect high pollution… Which turns out is mostly from me cooking.
Your HEPA filters must be real ones. HEPA is just an acronym anyone can slap on anything, there's no accreditation.
Recent testing on the Vacuum Wars channel showed big differences between filters from the vacuum manufacturer and off-brand "HEPA" filters. Probably the same applies everywhere.
"You need HEPA" is just marketing. What you really need is CADR (Clean Air Delivery Rate) and third-party testing.
HEPA H13 only means the filter was tested to 99.97% particle efficiency at the most difficult particle size. There's nothing magical about this number. In reality air filters can often clean better with an E11 or E12 filter (tested to 95% and 99.5% respectively), because these filters allow much greater airflow from the same fan.[0]
Remember, the clean air is immediately mixing with the dirty room air. If you get twice the airflow while "only" letting 5% of particles through, that's a good tradeoff.
CADR (tested by AHAM, not just the manufacturer's claim!) is what really matters, not HEPA vs non-HEPA.
> HEPA is just an acronym anyone can slap on anything, there's no accreditation.
There are standards:
> Filters meeting the HEPA standard must satisfy certain levels of efficiency. Common standards require that a HEPA air filter must remove—from the air that passes through—at least 99.95% (ISO, European Standard)[4][5] or 99.97% (ASME, U.S. DOE)[6][7] of particles whose diameter is equal to 0.3 μm, with the filtration efficiency increasing for particle diameters both less than and greater than 0.3 μm.[8]
I think the next big thing is going to be fixing cooking air pollution. Now that smoking has been in freefall it's becoming increasingly clear that cooking is the next big issue for lung cancers. Especially anything smoky or on a gas stove. It wouldn't be terribly impractical to put a much higher power extraction fan and some side walls to create a kind of fume hood like you'd get in a lab.
Years ago I lived in an apartment where the vent hood above the range was an overpowered commercial unit instead of the usual home stuff. It genuinely surprised me how much of a difference it made compared to 'normal' vent hoods. Higher extraction volumes, even without side walls, makes a big difference.
For around 2k it is possible to install a vent hood with the fan outside the building so it is completely silent, and has way more air flow than anything that fits above the range.
Complete silence, performance beyond anything people are used to at home. Most people don't even know the choice exists, and even if you go to a bougie specialty cooking store they'll try to dissuade you from this and instead sell you on a higher priced product that doesn't work as well.
What's annoying with both air cleaners and vent hoods, is that it seems some sellers have figured out that they want them to make noise, so people hear they are working. It's possible to make both much more quiet than they typically are.
One of the first upgrades I made to my house was buying a nice (interior) vent hood. The exterior ones need to be at least a few feet away from the stove, and my stove is right up against the wall it vents out of. I still was able to find an interior one that has 1/2 the noise and twice the airflow of the standard builder grade vent hood.
One annoyance is that almost none of the vent hood stick out far enough, ideally you want the vent hood to stick out a few inches (at least) past the front of the cook top, but almost none of them do that (likely due to head bumping issues, understandable) so a lot of effluent still escapes.
Higher extraction volumes also make heating and cooling bills go up.
It's one of those ideas that works fine when it's just a rare thing, but if 100% of households had one I guarantee we'd see headlines like "Wasteful Exhaust Vents Burn As Much Energy As Cleveland" etc etc.
I for one welcome our fume hood inspired overlords. The nice thing about fume hoods is that they're optimized for maximum extraction efficiency for a minimum extraction volume.
Everyone notices the side walls, but an overlooked secret of fume hoods is that they extract air backwards toward the back wall, not just upward.
Any air extraction pulls conditioned air out of the house - kitchen hoods, dryers, bath fans, etc. Only kitchen hoods exhaust a significant amount of air - the solution is a makeup air system.
The EPA estimates that radon[1] is the second leading cause of lung cancer after smoking. I have a RadonEye monitor in the basement. They aren't that expensive and it's nice to have the piece of mind.
A radon sensor is just an alpha radiation detector. There's little reason to distrust companies making them. You don't even really need very good calibration, you just want to know if radon levels exceed some "you should take action" treshold. Real-time radon detection is really a bit overkill.
For those interested the cheap option is box fan, something like this or duct tape https://a.co/d/3BEXNGp and a hepa filter. Works great and costs about 50 bucks.
Breathing and sleeping in negative ionized air for 40 years. Just high voltage potential -7 to -10kVDC and spread carbon hairs (better than metal spikes) to launch it.
Walls and floors always have positive charge conducted from the ground outside relative to the air, no sparks means ozone in too small concentrations to worry about. Dust, smoke, bacteria and viruses stick to walls not the inside of lungs and the air is clean and odorless. You can shine a very bright flashlight through it in a dark room and see absolutely no beam. Every so often you sponge off the walls with strong cleaning solution. Latex paint stains easily near the device which is a subtle way of reminding you how germy it really would have been. Use plastic over walls near the device to save yourself some color matching and painting.
Over all these years, the most annoying thing has been other people trying to sell me HEPA filter solutions with screaming fans that need accessory replacement often. They insist I'm killing myself with ozone as a fear tactic. Few people sell just ionizers or sabotage the concept by selling weak/ineffective ones... because HEPA is big money.
Ionizers use tiny energy and no recurring supplies. Just make sure your electronics are grounded well.
My primary device is a 2010 Comtech (good luck finding one). It's just a voltage multiplier off of 110VAC( https://en.wikipedia.org/wiki/Voltage_multiplier ). I bought 8 $5/ea Chinese 'neg ion modules' and tied then to the back of the fan... they are parts to build into a much weaker device for cars. They will last longer (because they're resin sealed) and safer (12VDC supply) but by comparative output measurement I will need an array of 36 to match the output of the 2010 device. At $5 ea, this is doable. There are single power supply units more capable but I like the idea of 36 separate waterproof replaceable 12VDC things.
No, I just know the mechanism (UV/spark) is missing and the air has no odor of it. I know the smell of O3 because an old boss had one of those cracking sparking monsters that projected blue on the ceiling when the light was off. It blew its power supply in short order and no one suffered ill effects, but no one missed it either.
I watched a grand designs episode where the parents (well, inflicted by the wife) Munchausen by proxied these allergies onto their kids. They were obsessive about having an allergy free house and spent hundreds of thousands building one with, basically a lesser version of what you explained up there.
Revisiting several years later, the children had integrated with society (amazing that they weren’t homeschooled) and lo and behold - allergy free.
The provocative host coaxed out of the parents that they believed that the house did bugger all in terms of helping their children.
I wonder how the kids are doing now without their namby mother
In 2023 there was a conference about Chemistry of Indoor Environments (CIE) that looked at the research that was done over a ten-year period; opening presentation:
Generally: avoid any use of electronics to 'do stuff' to the air or pathogens (e.g. UV) and just use high-MERV / HEPA filters, and use an ERV to vent stale air and bring in (filtered, conditioned) outside air.
Even HEPA isn’t a requirement, you just need a high CADR. Doesn’t matter if the filter doesn’t catch a particle on the first pass as long as it does one a subsequent one and the flow rate is high!
Yeah the whole 'just use HEPA' has been what's worked for us after about a half dozen different air purifiers of experimentation. I noticed the positive ionization things changed my heart rate variability which was spooky.
Empirically, no it doesn't, at least not for the quantities of smoke we get in wildfire season. It's probably enough for most "abandoned industry on fire again" fires, if that's all you get?
> Upgrading to a filter rated MERV 13 or higher can be especially important during smoky periods to effectively remove fine particle pollution from smoke in the indoor air.
The main challenge is the resistance to airflow (US: inches w.c.) that can be a problem with for HVAC equipment, which is why you want a large surface area, e.g.:
All the tech in the world won't change anything if people don't focus on airflow and airchanges. Air needs to move and be replenished with air from the outside. Filters/UV/etc are just a bonus.
Even basic airflow understanding is surprisingly not common knowledge. IE for air to leave a room occupied by humans, then air needs a path into that room too.
I commonly see ceiling exhaust fans in bathroom showers and toilets with windows sealed shut. The door is meant to be closed... so the only gap for air to come into the room is around the door somehow - while the exhaust fan struggles.
I even visited one host who implemented a seal along the bottom of the door because:
1. Shower creates steam and with the above mentioned little airflow, that steam stayed around.
2. So the exhaust fan had to run while they dried themselves with a towel.
3. But they didn't like getting cold feet from the draft of air coming in under the door...
I could not convince them they needed an air intake vent. :-(
Similar but different, a couple of times now I've been in hotel rooms with a bar fridge buzzing away entirely enclosed in a cupboard. Extrapolate that to the hundred rooms or more of the hotel and it is a colossal waste thanks to a "simple" understanding of airflow.
> I commonly see ceiling exhaust fans in bathroom showers and toilets with windows sealed shut. The door is meant to be closed... so the only gap for air to come into the room is around the door somehow
If the building has central air heating or cooling, having a vent into the bathroom is standard. That’s more than enough for the exhaust fan to pull from.
In areas where central air is uncommon, you need a decent door undercut. A surprising amount of air can flow around a door and modern exhaust fans can pull a relatively good vacuum.
I live in an apartment above a busy road, and my building has no central HVAC. Opening my windows makes the air (much, much) worse.
It took a while to figure this out, so from the ~1.5 years I've lived here, I've accumulated huge, thick coats of brake dust on my windowsills, in my carpets, on the blades of my air-circulation floor... and so on. Probably am half-way to developing COPD.
I do still "replenish air from outside", though! ...through a three-stage filter. (I put an industrial air scrubber on my balcony, and fed the exhaust from it inside through the same kind of doorjam seal you'd use for a portable AC unit.)
I still get noxious fumes coming in sometimes, though. I had to set the thing up on a timer so it wouldn't pull air in during rush hour.
I've been running an airgradient sensor for a year now and as a result I am seriously considering adding a MERV to my HVAC system. Ideally I'd like to get two more sensors (one outside, one in the HVAC ducts) and setup home assistant to govern air exchanges.
Tip: avoid the cheap 1" filters that only have a few pleats. Fewer pleats = less surface area = more flow resistance.
Many HVAC people will recommend thicker filters (3-6" thick) if using a higher MERV, but the 1" 3M 1900 often has more actual surface area if laid flat.
Testing by Project Farm and others showed the 3M 1900 filter has the lowest airflow resistance of any 1" high-MERV filter. If your HVAC only accepts a 1" filter, that's the only brand I'd use. Change the filter ideally every 3 months, but to avoid costly HVAC repairs don't exceed 6 months maximum.
You can damage/destroy your furnace if you put in a too restrictive filter. Better to follow manufacturer recommendations and add circulating air filters in your house.
> * Air needs to move and be replenished with air from the outside. Filters/UV/etc are just a bonus.*
Outside air needs to be filtered otherwise you can bring in pollen and other things (e.g., exhaust/brake dust from cars if near heavy arteries). Avoid UV for residences:
Yes, there is a whole certification system for measuring how well an air purifier works (CADR - Clean Air Delivery Rate) but consumers are easily distracted and confused by flashy features that promise everything but usually don't do much.
Who in the world is installing UV in forced air systems without running an activated carbon filter to remove ozone? The guides I followed when I installed mine called this out multiple times.
There doesn't need to be tests on humans. We have plenty of research showing that viruses harm humans as do small particles in the air this isn't in question at all. These devices have been shown to remove these items from the air using engineering testing based on physics like the electrostatic force and the laws of motion. That they work is not in question, they do filter the air.
The only remaining aspect is how well do they clear air that is constantly getting dirty that has been tested as well, for the most part 6 air changes an hour seems to drastically reduce the particle count.
The problem with medical research "questions" on filtration currently is it thinks random control trials are the gold standard of proof. They aren't physics and engineering tests are a much higher quality of science and evidence. Filters work, respirators do work to remove viruses because we know the size of aerosol they tend to live in (1-5 microns mostly for something like Covid) and how effective the filters are at those particle sizes.
this is similar to anti-vax propoganda - setting an ever higher bar and saying we need that first there is no particular reason to think lab tests are not most of what we need.
I don't really know if they help to prevent infections but my wife has Long Covid and every time there is too much dust, pollen or smoke around us she gets pretty bad.
So we decided to buy them with little proof after she noticed she feels somewhat better when staying in a room with one. It could even be partially placebo but for the days with too much particles from outside I think it really helps.
Maybe we should rather have a full control of air flows in our home but that would be a huge investment for a very old house, also having air flowing with windows partially open on dry days also seems to help. Humidity ( and certainly mold) also has a clear negative effect so I had to buy a dehumidifier too
I think it's worth mentioning to people that for non-infection purposes, HEPA is honestly not a great idea.
The problem is that such low-porosity filters struggle to even let air move through them. And if you don't move a lot of air, you aren't cleaning a lot of air. At low fan speeds they're effectively placebo for how little they do.
You can get around this by adding yet more powerful fans and cranking up their speed, but then it sounds like a jet engine. Everyone just ends up turning them off (or way down) because they're too noisy - defeating the purpose.
If you just want non-virus stuff (pollen, smoke, dust) then don't go HEPA. Go with something like MERV-13. They come in standard off the shelf furnace style filters. They're way cheaper than HEPA and way better for most use cases.
HEPA only makes sense for something as fine as viruses, or if you only get a single pass to do the filtering. For anything that circulates (like in a house) it makes 0 sense.
Fair argument, but let’s not forget that indoor air quality, HEPA filters, and upper air UV systems weren’t even allowed to be discussed as solutions to airborne transmission of viruses not that long ago. It was all about masks/no masks, remember? It’s a little unfair to say that things haven’t been studied, when it would have been career damaging to do so until very recently.
This is baloney? Air quality experts like Richard Corsi (UC Davis, now, poor guy, the dean of the college of engineering) have been advocating for increasing both external ACH (air changes/hour) and filtration ACH since nearly the beginning of the pandemic.
> Early in the pandemic, his efforts focused on lowering inhalation dose of virus-laden aerosol particles indoors. He led an effort to develop an educational tool for assessing parallel interventions for lowering inhalation dose for aerosols and risk of infection in buildings. His concept of a low-cost and effective do-it-yourself air cleaner to combat virus-laden aerosol particles and wildfire smoke has become known worldwide as the Corsi-Rosenthal Box. He recently chaired a National Academies committee responsible for the 2024 report, “Health Risks of Indoor Exposure to Fine Particulate Matter and Practical Mitigation Solutions.”
An awful lot of people who pay attention to engineering solutions for airborne risk reduction - the people who know what ASHRAE is - were saying exactly the same thing throughout nearly the entirety of the pandemic. Because of their advocacy and data, as one example, we got HEPA filters installed in our kids' elementary and preschools as part of the strategy to resume in-person education.
Got a source? I don't remember anyone objecting to studying HEPA filters' impact on airborne viruses. In fact, I've found studies on that exact topic from that time period. The CDC was saying that HEPA combined with masks was more effective than masking alone back in 2021 (but masking alone was better than HEPA alone)
> Without the HEPA air cleaners, universal masking reduced the combined mean aerosol concentration by 72%. The combination of the two HEPA air cleaners and universal masking reduced overall exposure by up to 90%. The HEPA air cleaners were most effective when they were close to the aerosol source
Yep, I agree. Other comments here seem to display a collective amnesia but there was very clearly a mandatory authoritarian single solution to COVID and alternatives were not allowed to be considered even if they were good substitutes. Bringing up alternatives would get you censored or banned or just attacked.
Karolinska Institute in Sweden did a study during the pandemic that had findings of virus particles in every location in the hospital ventilation system, past all filters and air purifying. It was a early finding that indicated the role of recycled air in spreading the virus in places like airports, planes, trains and large buildings like shopping malls. The covid virus is so small and so effective as a airborne virus that even hospital filters had a limited effect.
Smaller doesn't mean harder to filter, beyond a certain size. HN favorite (and pre-covid particulate filtrering proponent) dynomight explained this well in an article on a cheap air purifier:
Also, I'm pretty sure respiratory viruses need aerosol droplets to get anywhere they can harm you, and those droplets are much bigger than viruses anyway.
Some respiratory viruses need large aerosol droplets, but covid virus particles remaining viable with a half-life of up to about an hour outside large droplets.
The initial theory was that environments like extreme hot and humid climates made it impossible for aerosol droplets to harm people, while dry air increased the risk. This recommendation was change later into the pandemic as new evidence was gathered.
There are similar studies on influenza. There doesn't seem a strong consensus on what environments are safe, or how long such viruses can last outside of large droplets. There is a lot of factors in play, including the virus itself.
So this is why we were told to wear masks that were ineffective at blocking viruses? In short, we effectively went mask-less for the duration and spreading was relatively minimal; certainly not mitigated by disposable masks.
Fact: There was a brief moment during the pandemic when Faucci tipped his hand on the ineffectiveness of disposable masks. He did a week-ish of suggesting we wear TWO masks. The only reason to do that was - as a seasoned virologist - he KNEW one mask was not good enough. Why else would he do that?
Let’s just say “the science” we were fed during COVID was lacking in a number of ways.
Please note: The above our not my opinion. These are real things that happened. Please don’t down vote simple because you can’t come to terms with your cognitive dissonance.
Respiratory virus particles outside an aerosol droplet don't last long, but yes, they should be filtered too (not "blocked", it will always be probabilistic)
No it isn't actually, those kind of low level technical questions have been somewhat studied. It's the end to end interventions which have been poorly studied.
No I don't. What I remember is that they said a lot about social distancing and going outside, and for those who do have to be around others, they initially said you gotta wear N95 since ordinary masks aren't very effective, then they said there's a shortage of N95 masks so please just wear normal masks since at least it's better than nothing, and save the N95s for the hospitals and other high-risk settings/workers.
If you remember it differently, please explain what I'm misremembering, because (unlike a sizable fraction of the population) I don't remember hearing anything nonsensical or misleading about masks, especially given the information and resources they had available at the time.
California was forcing people to go indoors from the beach after we at HN were discussing the misleading CDC recommendations that masks won’t help… it really depends on what timeline you focus on.
> California was forcing people to go indoors from the beach after we at HN were discussing the misleading CDC recommendations that masks won’t help
What does that have to do with masks?
And wasn't this in the beginning of the lockdown while they were scrambling to figure things out?
And "misleading" in what way? I know you and the rest of HN knew exactly the right thing to do in the very start of lockdown, so it's sad that they never came on HN for advice, but what makes you think they knew a better solution and yet held it from you?
No, I do not remember that. I'm pretty sure you just made it up. Air filtering is obviously long-studied, and if you are alluding to COVID-era events I seem to recall that one of the first large-scale responses that happened in my region was the subway operator installed up-rated HEPA+UV air cleaners on every car.
If you want to sustain this claim, show us the process by which someone's career was truncated by researching air filtration.
You're clearly pushing an agenda. The problem is that these kind of filtration systems couldn't be rolled out en-masse across the world.
During COVID hospitals absolutely were using air filtration systems and places where it made sense (I remember COVID doctor's conferences had advanced filters for each room).
Every jurisdiction had an overreaction fetish. Masks, social distancing and vaccine cards on the left. Ivermectin, detergent pods and intentional exposure on the right.
Maybe there was one with an anti-air filter message. But between New York, the Bay Area, Arizona, Tennessee, Wyoming, London, Frankfurt and New Delhi, I didn’t see it.
Double blind studies are helpful when we do not understand they underlying dynamics of a complicated system (like a body) but we want to learn what effect a change has on that system (like a medicine).
If we know pathogens cause disease, and we know filtering removes pathogens from the air (and we can test and verify that) we don't need to run a double blind study to verify they work.
It's the same reason you don't need to run a double blind study on whether seat belts work. We understand the cause and effect of car ejections and windshield/steering wheel impacts on human bodies. Seat belts are designed to mitigate these incidents and are tested and validated in the lab using formal science and engineering.
> It's the same reason you don't need to run a double blind study on whether seat belts work.
We might need some historical investigation into the road that was travelled to get seatbelts to where they are now (physically, legally, and socially). I'm a millennial and I remember growing up where similar arguments were made:
- "If it's my time to go, then it's God's will"
- "It's uncomfortable"
- zero/inconsistent law enforcement
- "If the car rolls over than it can trap you"
To now, where it's entirely automatic and incredibly wild to even suggest being without a seatbelt.
Don't forget the one about how it's safer to be thrown free of a wreck (which will happen if you don't wear your seatbelt) than remain in the car. <sigh>
Its crazy, I was born in the early 80s and I never wore a seatbelt until I started driving. As a kid I would ride in a van that didn't even have seats and think absolutely nothing of it.
I was born in the early 70s and we always wore seatbelts, for as long as I can remember. Though we did routinely ride in the back of the pickup, which isn't something I see happening much today.
You're not going to spend 100% of your day in the coverage of one of these things, so what's the dose response? How many hours per day of filtered air equals how many fewer infections per year? Does air filtration in your workplace matter at all if you have young kids in school? Does air filtration in a school matter at all if the kids are all together on a poorly ventilated bus for two hours a day?
Seems like some evidence would be helpful.
Yes we have studied actual rates of infection in response to interventions like air filtering, so these studies account for all that real-world complexity and messiness you worry about.
The article is complaining that every study doesn't redo the evidence collection, end-to-end, every time. That's not realistic and not necessary.
A lot of your specific questions are leading (with a nothing-we-can-do attitude underneath) or asking the wrong question (eg expecting one universal number for "hours of filtration per infection prevented").
For instance the correct answer may be air filters in classrooms and buses and workplaces, but strangely your line of questioning doesn't even consider that possibility.
This would be like someone in the 1800s questioning how handwashing avoids Cholera if they don't wash their hands at home. I think I see a solution to this one...
Kids don’t transmit tire and brake dust into my lungs
> It's the same reason you don't need to run a double blind study on whether seat belts work
Actually, seat belts are a weird example. After they were invented, there were more car crashes since people trusted they were protected. Without seat belts people were more cautious. They were a net positive of course, but some different situations/inventions/studies might have effects that are the opposite of what you would expect.
That’s a myth https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1540-6237....
I support more research but anecdotally HEPA air filters changed my life. I used to get pretty bad respiratory infections every winter but after getting these that went away. I’m talking the simple kind with basic charcoal prefilter and fiber HEPA filter which are about $150 at most home stores or big box stores. Never used any ionization or ozone. The interesting bit is the newer ones even measure air particulates and have a variable speed option where they will speed up when they detect high pollution… Which turns out is mostly from me cooking.
Your HEPA filters must be real ones. HEPA is just an acronym anyone can slap on anything, there's no accreditation.
Recent testing on the Vacuum Wars channel showed big differences between filters from the vacuum manufacturer and off-brand "HEPA" filters. Probably the same applies everywhere.
https://www.youtube.com/watch?v=eAIYRykQkMk
HEPA H13 only means the filter was tested to 99.97% particle efficiency at the most difficult particle size. There's nothing magical about this number. In reality air filters can often clean better with an E11 or E12 filter (tested to 95% and 99.5% respectively), because these filters allow much greater airflow from the same fan.[0]
Remember, the clean air is immediately mixing with the dirty room air. If you get twice the airflow while "only" letting 5% of particles through, that's a good tradeoff.
CADR (tested by AHAM, not just the manufacturer's claim!) is what really matters, not HEPA vs non-HEPA.
[0] https://x.com/Engineer_Wong/status/1899144721710408038
> HEPA is just an acronym anyone can slap on anything, there's no accreditation.
There are standards:
> Filters meeting the HEPA standard must satisfy certain levels of efficiency. Common standards require that a HEPA air filter must remove—from the air that passes through—at least 99.95% (ISO, European Standard)[4][5] or 99.97% (ASME, U.S. DOE)[6][7] of particles whose diameter is equal to 0.3 μm, with the filtration efficiency increasing for particle diameters both less than and greater than 0.3 μm.[8]
* https://en.wikipedia.org/wiki/HEPA
* https://en.wikipedia.org/wiki/HEPA#Specifications
Here in India you can usually tell them apart by whether they are advertised as HEPA vs "HEPA-type".
I think the next big thing is going to be fixing cooking air pollution. Now that smoking has been in freefall it's becoming increasingly clear that cooking is the next big issue for lung cancers. Especially anything smoky or on a gas stove. It wouldn't be terribly impractical to put a much higher power extraction fan and some side walls to create a kind of fume hood like you'd get in a lab.
Years ago I lived in an apartment where the vent hood above the range was an overpowered commercial unit instead of the usual home stuff. It genuinely surprised me how much of a difference it made compared to 'normal' vent hoods. Higher extraction volumes, even without side walls, makes a big difference.
For around 2k it is possible to install a vent hood with the fan outside the building so it is completely silent, and has way more air flow than anything that fits above the range.
Complete silence, performance beyond anything people are used to at home. Most people don't even know the choice exists, and even if you go to a bougie specialty cooking store they'll try to dissuade you from this and instead sell you on a higher priced product that doesn't work as well.
What's annoying with both air cleaners and vent hoods, is that it seems some sellers have figured out that they want them to make noise, so people hear they are working. It's possible to make both much more quiet than they typically are.
One of the first upgrades I made to my house was buying a nice (interior) vent hood. The exterior ones need to be at least a few feet away from the stove, and my stove is right up against the wall it vents out of. I still was able to find an interior one that has 1/2 the noise and twice the airflow of the standard builder grade vent hood.
One annoyance is that almost none of the vent hood stick out far enough, ideally you want the vent hood to stick out a few inches (at least) past the front of the cook top, but almost none of them do that (likely due to head bumping issues, understandable) so a lot of effluent still escapes.
Higher extraction volumes also make heating and cooling bills go up.
It's one of those ideas that works fine when it's just a rare thing, but if 100% of households had one I guarantee we'd see headlines like "Wasteful Exhaust Vents Burn As Much Energy As Cleveland" etc etc.
I for one welcome our fume hood inspired overlords. The nice thing about fume hoods is that they're optimized for maximum extraction efficiency for a minimum extraction volume.
Everyone notices the side walls, but an overlooked secret of fume hoods is that they extract air backwards toward the back wall, not just upward.
Any air extraction pulls conditioned air out of the house - kitchen hoods, dryers, bath fans, etc. Only kitchen hoods exhaust a significant amount of air - the solution is a makeup air system.
The EPA estimates that radon[1] is the second leading cause of lung cancer after smoking. I have a RadonEye monitor in the basement. They aren't that expensive and it's nice to have the piece of mind.
[1] https://www.epa.gov/radon/health-risk-radon
What lead you to trust RadonEye?
A radon sensor is just an alpha radiation detector. There's little reason to distrust companies making them. You don't even really need very good calibration, you just want to know if radon levels exceed some "you should take action" treshold. Real-time radon detection is really a bit overkill.
I wonder how one could validate a radon detector. Can one buy a phial known air/radon concentration online without ending up on some spooky list?
Naturally, you would have to account what changes in the sample during shipping, due to the short half-life...
> how one could validate a radon detector
Get a professional measurement and compare. This Reddit thread gave me pause [1].
[1] https://www.reddit.com/r/radon/comments/ptz8tt/professional_...
For those interested the cheap option is box fan, something like this or duct tape https://a.co/d/3BEXNGp and a hepa filter. Works great and costs about 50 bucks.
Well you will need a particulate detector to determine the problem and then that will inform your solution.
Breathing and sleeping in negative ionized air for 40 years. Just high voltage potential -7 to -10kVDC and spread carbon hairs (better than metal spikes) to launch it.
Walls and floors always have positive charge conducted from the ground outside relative to the air, no sparks means ozone in too small concentrations to worry about. Dust, smoke, bacteria and viruses stick to walls not the inside of lungs and the air is clean and odorless. You can shine a very bright flashlight through it in a dark room and see absolutely no beam. Every so often you sponge off the walls with strong cleaning solution. Latex paint stains easily near the device which is a subtle way of reminding you how germy it really would have been. Use plastic over walls near the device to save yourself some color matching and painting.
Over all these years, the most annoying thing has been other people trying to sell me HEPA filter solutions with screaming fans that need accessory replacement often. They insist I'm killing myself with ozone as a fear tactic. Few people sell just ionizers or sabotage the concept by selling weak/ineffective ones... because HEPA is big money.
Ionizers use tiny energy and no recurring supplies. Just make sure your electronics are grounded well.
Do you have a more detailed writeup about how you've set this up?
My primary device is a 2010 Comtech (good luck finding one). It's just a voltage multiplier off of 110VAC( https://en.wikipedia.org/wiki/Voltage_multiplier ). I bought 8 $5/ea Chinese 'neg ion modules' and tied then to the back of the fan... they are parts to build into a much weaker device for cars. They will last longer (because they're resin sealed) and safer (12VDC supply) but by comparative output measurement I will need an array of 36 to match the output of the 2010 device. At $5 ea, this is doable. There are single power supply units more capable but I like the idea of 36 separate waterproof replaceable 12VDC things.
Ozone is bad for you though. How do you manage that?
Edit: Sorry, you did address that.
> no sparks means ozone in too small concentrations to worry about.
Have you actually measured?
No, I just know the mechanism (UV/spark) is missing and the air has no odor of it. I know the smell of O3 because an old boss had one of those cracking sparking monsters that projected blue on the ceiling when the light was off. It blew its power supply in short order and no one suffered ill effects, but no one missed it either.
Can you recommend any devices?
There's HEPA, then there's high voltage ionizers, then there's PCO purifiers. PCO seems to have some advantages over ionizers.
Are you allergic to going outside?
I watched a grand designs episode where the parents (well, inflicted by the wife) Munchausen by proxied these allergies onto their kids. They were obsessive about having an allergy free house and spent hundreds of thousands building one with, basically a lesser version of what you explained up there.
Revisiting several years later, the children had integrated with society (amazing that they weren’t homeschooled) and lo and behold - allergy free.
The provocative host coaxed out of the parents that they believed that the house did bugger all in terms of helping their children.
I wonder how the kids are doing now without their namby mother
In 2023 there was a conference about Chemistry of Indoor Environments (CIE) that looked at the research that was done over a ten-year period; opening presentation:
* https://www.youtube.com/watch?v=vt0GLbi20Q4
* https://indoorchem.org/publications/
Playlist of the various presentations from the conference:
* https://www.youtube.com/watch?v=J2iHOCI2hz4&list=PLsc2-5fAgM...
Generally: avoid any use of electronics to 'do stuff' to the air or pathogens (e.g. UV) and just use high-MERV / HEPA filters, and use an ERV to vent stale air and bring in (filtered, conditioned) outside air.
Even HEPA isn’t a requirement, you just need a high CADR. Doesn’t matter if the filter doesn’t catch a particle on the first pass as long as it does one a subsequent one and the flow rate is high!
Yeah the whole 'just use HEPA' has been what's worked for us after about a half dozen different air purifiers of experimentation. I noticed the positive ionization things changed my heart rate variability which was spooky.
Empirically, the ionizer is good for wildfire season, but the rest of the year HEPA is good.
> Empirically, the ionizer is good for wildfire season, but the rest of the year HEPA is good.
Smoke can be dealt with via a carbon filter and you don't have to do a chemistry experiment in your house.
* https://shop.aprilaire.com/search?q=Carbon+Air+Filter
Empirically, no it doesn't, at least not for the quantities of smoke we get in wildfire season. It's probably enough for most "abandoned industry on fire again" fires, if that's all you get?
Per the EPA:
> Upgrading to a filter rated MERV 13 or higher can be especially important during smoky periods to effectively remove fine particle pollution from smoke in the indoor air.
* https://www.epa.gov/wildfire-smoke-course/preparing-fire-sea...
The carbon is for the smell. The EPA also points to this California list, which include "mechanical" types which do not use electronic measures:
* https://ww2.arb.ca.gov/list-carb-certified-air-cleaning-devi...
The main challenge is the resistance to airflow (US: inches w.c.) that can be a problem with for HVAC equipment, which is why you want a large surface area, e.g.:
* https://electronicaircleaners.com/docs/aprilaire_2416_2216_a...
* https://www.aprilaire.com/whole-house-products/air-purifiers...
All the tech in the world won't change anything if people don't focus on airflow and airchanges. Air needs to move and be replenished with air from the outside. Filters/UV/etc are just a bonus.
> if people don't focus on airflow and airchanges
Even basic airflow understanding is surprisingly not common knowledge. IE for air to leave a room occupied by humans, then air needs a path into that room too.
I commonly see ceiling exhaust fans in bathroom showers and toilets with windows sealed shut. The door is meant to be closed... so the only gap for air to come into the room is around the door somehow - while the exhaust fan struggles.
I even visited one host who implemented a seal along the bottom of the door because:
1. Shower creates steam and with the above mentioned little airflow, that steam stayed around.
2. So the exhaust fan had to run while they dried themselves with a towel.
3. But they didn't like getting cold feet from the draft of air coming in under the door...
I could not convince them they needed an air intake vent. :-(
Similar but different, a couple of times now I've been in hotel rooms with a bar fridge buzzing away entirely enclosed in a cupboard. Extrapolate that to the hundred rooms or more of the hotel and it is a colossal waste thanks to a "simple" understanding of airflow.
> I commonly see ceiling exhaust fans in bathroom showers and toilets with windows sealed shut. The door is meant to be closed... so the only gap for air to come into the room is around the door somehow
If the building has central air heating or cooling, having a vent into the bathroom is standard. That’s more than enough for the exhaust fan to pull from.
In areas where central air is uncommon, you need a decent door undercut. A surprising amount of air can flow around a door and modern exhaust fans can pull a relatively good vacuum.
Yeah, the real pro tip here is sealing the bottom of your bathroom door to avoid cold feet. Genius!
> be replenished with air from the outside
I live in an apartment above a busy road, and my building has no central HVAC. Opening my windows makes the air (much, much) worse.
It took a while to figure this out, so from the ~1.5 years I've lived here, I've accumulated huge, thick coats of brake dust on my windowsills, in my carpets, on the blades of my air-circulation floor... and so on. Probably am half-way to developing COPD.
I do still "replenish air from outside", though! ...through a three-stage filter. (I put an industrial air scrubber on my balcony, and fed the exhaust from it inside through the same kind of doorjam seal you'd use for a portable AC unit.)
I still get noxious fumes coming in sometimes, though. I had to set the thing up on a timer so it wouldn't pull air in during rush hour.
I've been running an airgradient sensor for a year now and as a result I am seriously considering adding a MERV to my HVAC system. Ideally I'd like to get two more sensors (one outside, one in the HVAC ducts) and setup home assistant to govern air exchanges.
Tip: avoid the cheap 1" filters that only have a few pleats. Fewer pleats = less surface area = more flow resistance.
Many HVAC people will recommend thicker filters (3-6" thick) if using a higher MERV, but the 1" 3M 1900 often has more actual surface area if laid flat.
Testing by Project Farm and others showed the 3M 1900 filter has the lowest airflow resistance of any 1" high-MERV filter. If your HVAC only accepts a 1" filter, that's the only brand I'd use. Change the filter ideally every 3 months, but to avoid costly HVAC repairs don't exceed 6 months maximum.
You can damage/destroy your furnace if you put in a too restrictive filter. Better to follow manufacturer recommendations and add circulating air filters in your house.
> * Air needs to move and be replenished with air from the outside. Filters/UV/etc are just a bonus.*
Outside air needs to be filtered otherwise you can bring in pollen and other things (e.g., exhaust/brake dust from cars if near heavy arteries). Avoid UV for residences:
* https://www.youtube.com/watch?v=xLwHmfdwO9s
Or for anyone on the west coast the last 5 years, nasty smoke.
Carbon filters on your incoming air supply (e.g., ERV):
* https://shop.aprilaire.com/search?q=Carbon+Air+Filter
1) broken link 2) any (actual) HEPA filter works too.
A lot of stuff sold as HEPA doesn’t meet the original HEPA standards though, so needs to be actually rated for the super small particles.
Toronto also
Yes, there is a whole certification system for measuring how well an air purifier works (CADR - Clean Air Delivery Rate) but consumers are easily distracted and confused by flashy features that promise everything but usually don't do much.
If by ‘people’ you mean ‘mechanical engineers’, they already do, see ASHRAE 62.1 - Ventilation and Acceptable Indoor Air Quality
https://static1.squarespace.com/static/6320b844c3820725e4d56...
Who in the world is installing UV in forced air systems without running an activated carbon filter to remove ozone? The guides I followed when I installed mine called this out multiple times.
I’ve just been pip installing my forced air systems and it’s been going ok
Not all UV wavelengths generate ozone.
There doesn't need to be tests on humans. We have plenty of research showing that viruses harm humans as do small particles in the air this isn't in question at all. These devices have been shown to remove these items from the air using engineering testing based on physics like the electrostatic force and the laws of motion. That they work is not in question, they do filter the air.
The only remaining aspect is how well do they clear air that is constantly getting dirty that has been tested as well, for the most part 6 air changes an hour seems to drastically reduce the particle count.
The problem with medical research "questions" on filtration currently is it thinks random control trials are the gold standard of proof. They aren't physics and engineering tests are a much higher quality of science and evidence. Filters work, respirators do work to remove viruses because we know the size of aerosol they tend to live in (1-5 microns mostly for something like Covid) and how effective the filters are at those particle sizes.
this is similar to anti-vax propoganda - setting an ever higher bar and saying we need that first there is no particular reason to think lab tests are not most of what we need.
I have 3 oversized air purifiers in my home.
I don't really know if they help to prevent infections but my wife has Long Covid and every time there is too much dust, pollen or smoke around us she gets pretty bad.
So we decided to buy them with little proof after she noticed she feels somewhat better when staying in a room with one. It could even be partially placebo but for the days with too much particles from outside I think it really helps.
Maybe we should rather have a full control of air flows in our home but that would be a huge investment for a very old house, also having air flowing with windows partially open on dry days also seems to help. Humidity ( and certainly mold) also has a clear negative effect so I had to buy a dehumidifier too
I think it's worth mentioning to people that for non-infection purposes, HEPA is honestly not a great idea.
The problem is that such low-porosity filters struggle to even let air move through them. And if you don't move a lot of air, you aren't cleaning a lot of air. At low fan speeds they're effectively placebo for how little they do.
You can get around this by adding yet more powerful fans and cranking up their speed, but then it sounds like a jet engine. Everyone just ends up turning them off (or way down) because they're too noisy - defeating the purpose.
If you just want non-virus stuff (pollen, smoke, dust) then don't go HEPA. Go with something like MERV-13. They come in standard off the shelf furnace style filters. They're way cheaper than HEPA and way better for most use cases.
HEPA only makes sense for something as fine as viruses, or if you only get a single pass to do the filtering. For anything that circulates (like in a house) it makes 0 sense.
UV-C / hydroxyl generators or bust
This is a "metastudy".
This is just "we have no evidence that masks prevent spread of disease" all over again.
Yes that's technically true, but this is just a grant money grab.
It's not a serious attempt to study these things.
Funded by National Institute for Occupational Safety and Health at the Centers for Disease Control and Prevention aka NIOSH / CDC
Which has been completely gutted by the current administration.
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>analyzed nearly 700 studies
Really feels like they went so meta here they lost the plot.
Complaints about fails to catch covid. People are buying air filters to fish out particulate matter not fix a 2022 pandemic.
To say they failed to see the forest for all the trees would be a kindness
Fair argument, but let’s not forget that indoor air quality, HEPA filters, and upper air UV systems weren’t even allowed to be discussed as solutions to airborne transmission of viruses not that long ago. It was all about masks/no masks, remember? It’s a little unfair to say that things haven’t been studied, when it would have been career damaging to do so until very recently.
This is baloney? Air quality experts like Richard Corsi (UC Davis, now, poor guy, the dean of the college of engineering) have been advocating for increasing both external ACH (air changes/hour) and filtration ACH since nearly the beginning of the pandemic.
> Early in the pandemic, his efforts focused on lowering inhalation dose of virus-laden aerosol particles indoors. He led an effort to develop an educational tool for assessing parallel interventions for lowering inhalation dose for aerosols and risk of infection in buildings. His concept of a low-cost and effective do-it-yourself air cleaner to combat virus-laden aerosol particles and wildfire smoke has become known worldwide as the Corsi-Rosenthal Box. He recently chaired a National Academies committee responsible for the 2024 report, “Health Risks of Indoor Exposure to Fine Particulate Matter and Practical Mitigation Solutions.”
An awful lot of people who pay attention to engineering solutions for airborne risk reduction - the people who know what ASHRAE is - were saying exactly the same thing throughout nearly the entirety of the pandemic. Because of their advocacy and data, as one example, we got HEPA filters installed in our kids' elementary and preschools as part of the strategy to resume in-person education.
What to supplement your understanding of COVID, schools, and myths vs facts? This was NPR The Pulse recently:
Back to School in a Rapidly Changing World
https://play.prx.org/listen?ge=prx_12369_085cdf46-2a33-4f24-...
Let just say, if you’re looking for baloney, this podcast (and the author / book it discusses) delivers. In short, we were gravely (?) misled.
Got a source? I don't remember anyone objecting to studying HEPA filters' impact on airborne viruses. In fact, I've found studies on that exact topic from that time period. The CDC was saying that HEPA combined with masks was more effective than masking alone back in 2021 (but masking alone was better than HEPA alone)
> Without the HEPA air cleaners, universal masking reduced the combined mean aerosol concentration by 72%. The combination of the two HEPA air cleaners and universal masking reduced overall exposure by up to 90%. The HEPA air cleaners were most effective when they were close to the aerosol source
Things changed alot, in 2020 the message was different because they were forced to admit they were wrong.
Yep, I agree. Other comments here seem to display a collective amnesia but there was very clearly a mandatory authoritarian single solution to COVID and alternatives were not allowed to be considered even if they were good substitutes. Bringing up alternatives would get you censored or banned or just attacked.
Karolinska Institute in Sweden did a study during the pandemic that had findings of virus particles in every location in the hospital ventilation system, past all filters and air purifying. It was a early finding that indicated the role of recycled air in spreading the virus in places like airports, planes, trains and large buildings like shopping malls. The covid virus is so small and so effective as a airborne virus that even hospital filters had a limited effect.
Smaller doesn't mean harder to filter, beyond a certain size. HN favorite (and pre-covid particulate filtrering proponent) dynomight explained this well in an article on a cheap air purifier:
https://dynomight.net/ikea-purifier/
Also, I'm pretty sure respiratory viruses need aerosol droplets to get anywhere they can harm you, and those droplets are much bigger than viruses anyway.
Some respiratory viruses need large aerosol droplets, but covid virus particles remaining viable with a half-life of up to about an hour outside large droplets.
The initial theory was that environments like extreme hot and humid climates made it impossible for aerosol droplets to harm people, while dry air increased the risk. This recommendation was change later into the pandemic as new evidence was gathered.
There are similar studies on influenza. There doesn't seem a strong consensus on what environments are safe, or how long such viruses can last outside of large droplets. There is a lot of factors in play, including the virus itself.
So this is why we were told to wear masks that were ineffective at blocking viruses? In short, we effectively went mask-less for the duration and spreading was relatively minimal; certainly not mitigated by disposable masks.
This was also interesting:
Back to School in a Rapidly Changing World
https://play.prx.org/listen?ge=prx_12369_085cdf46-2a33-4f24-...
> why we were told to wear masks that were ineffective at blocking viruses?
Masks and HEPA filters can block droplets that contain viruses. Neither filters out actual virus particles.
Fact: There was a brief moment during the pandemic when Faucci tipped his hand on the ineffectiveness of disposable masks. He did a week-ish of suggesting we wear TWO masks. The only reason to do that was - as a seasoned virologist - he KNEW one mask was not good enough. Why else would he do that?
https://www.today.com/health/dr-fauci-shows-how-wear-2-masks...
More recently, on NPR’s The Pulse was this:
Back to School in a Rapidly Changing World
https://play.prx.org/listen?ge=prx_12369_085cdf46-2a33-4f24-...
Let’s just say “the science” we were fed during COVID was lacking in a number of ways.
Please note: The above our not my opinion. These are real things that happened. Please don’t down vote simple because you can’t come to terms with your cognitive dissonance.
Respiratory virus particles outside an aerosol droplet don't last long, but yes, they should be filtered too (not "blocked", it will always be probabilistic)
> they should be filtered too (not "blocked", it will always be probabilistic)
The article’s point is we haven’t precisely studied what those probabilities are.
No it isn't actually, those kind of low level technical questions have been somewhat studied. It's the end to end interventions which have been poorly studied.
> It was all about masks/no masks, remember?
No I don't. What I remember is that they said a lot about social distancing and going outside, and for those who do have to be around others, they initially said you gotta wear N95 since ordinary masks aren't very effective, then they said there's a shortage of N95 masks so please just wear normal masks since at least it's better than nothing, and save the N95s for the hospitals and other high-risk settings/workers.
If you remember it differently, please explain what I'm misremembering, because (unlike a sizable fraction of the population) I don't remember hearing anything nonsensical or misleading about masks, especially given the information and resources they had available at the time.
California was forcing people to go indoors from the beach after we at HN were discussing the misleading CDC recommendations that masks won’t help… it really depends on what timeline you focus on.
> California was forcing people to go indoors from the beach after we at HN were discussing the misleading CDC recommendations that masks won’t help
What does that have to do with masks?
And wasn't this in the beginning of the lockdown while they were scrambling to figure things out?
And "misleading" in what way? I know you and the rest of HN knew exactly the right thing to do in the very start of lockdown, so it's sad that they never came on HN for advice, but what makes you think they knew a better solution and yet held it from you?
No, I do not remember that. I'm pretty sure you just made it up. Air filtering is obviously long-studied, and if you are alluding to COVID-era events I seem to recall that one of the first large-scale responses that happened in my region was the subway operator installed up-rated HEPA+UV air cleaners on every car.
If you want to sustain this claim, show us the process by which someone's career was truncated by researching air filtration.
> It was all about masks/no masks, remember?
You're clearly pushing an agenda. The problem is that these kind of filtration systems couldn't be rolled out en-masse across the world.
During COVID hospitals absolutely were using air filtration systems and places where it made sense (I remember COVID doctor's conferences had advanced filters for each room).
> It was all about masks/no masks, remember?
Every jurisdiction had an overreaction fetish. Masks, social distancing and vaccine cards on the left. Ivermectin, detergent pods and intentional exposure on the right.
Maybe there was one with an anti-air filter message. But between New York, the Bay Area, Arizona, Tennessee, Wyoming, London, Frankfurt and New Delhi, I didn’t see it.