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Smart Air (smartairfilters.com)
231 points by lispython on Nov 2, 2013 | hide | past | web | favorite | 91 comments

I never thought I'd be pulled in by a product that essentially bills itself as "Clean your air CHEAP with this one cool trick discovered by a college kid", but they've executed well.

What they're offering is just an easy way to buy a fan and HEPA filter ($27USD, or 166RMB, as the FAQ freely admits). Even so, their website makes me like instantly their business model, and because of their approach and willingness to run workshops, I immediately trust goods from them more than than I trust buying the parts directly from the manufacturer.

It will be interesting to see what they do with their new, loyal customer base. I imagine they could easily start a filter-replacement subscription service, where they send you as many new filters as you need for XXrmb/year. If you're needing more than is profitable, they could add a phone call into the process "to diagnose why your home is needing filters than it should". This is the kind of honor system that only works if your customers already like you. Assuming their product actually works, I think they will easily achieve that.

Hey, this is Thomas--Smart Air is my startup. Thanks for the ideas! I'll consider adding a subscription service. Several people told me at the beginning NOT to publish my findings (at http://particlecounting.tumblr.com/) because I should make money off of it instead. But I published it anyway because I thought (1) if I don't make a dime, but people learn how to protect their health without going broke, that alone is worth it and (2) there's space for an air filter company that publishes data openly.

There's so much trust involved in air filters because it's almost impossible to know if they're working if you don't have an expensive particle counter. So we're hoping that our open data and methods will show that they can protect their health without going broke.

Hi Thomas, I'm a Science and technology instructor for high school students in Beijing, this could make a great project for them. Call me at tianshuo_at_gmail_dot_com

This is a very neat idea, though I suspect they'll ultimately want a more powerful fan.

Note that high quality air filters also have a carbon pre-filter that gets changed more often than the HEPA filter, and having one ought to make your HEPA filter last much longer, especially in somewhere like Bejing. They also play a part in controlling odors.

This is what I'm currently using and love it to death. Note that the customer photos with the "dirty" filters are actually the carbon pre-filter and not the HEPA


I'm still trying to reconcile the $300 price tag of yours with the price tag of a carbon filter (5 on amazon) HEPA filter (70 on amazon) and box fan (30 on amazon). Is there really 200 dollars worth of plastic, assembly, marketing and IP in the the whispure? Or is there one important element I'm not accounting for (perhaps fan power, fan noise, some kind of PID, or sensors to check filter health)

a quote from the movie with the mock history of dr kellogs:

health is the easy way to a fool's wallet.

that said I have 3 expensive of those filter at my home. not that one, 3 other different brands. The main factor for my purchases were silence. and ironically the only one that was silent is a discontinued sharp model that sold for $150. all the $300 models are awful. specially the blueAir one that focus all it's marketing on being silent.

> health is the easy way to a fool's wallet

No it's not, especially with a preemptive health solution (solving a problem people don't feel they have).

You seem to be suggesting that pre-emptive health solutions are a very considered purchase, but isn't fear a major driver of such purchases? Perhaps not unwarranted fear, but fear is also not very conducive to completely rational purchasing behavior.

How do the three compare on size? I suspect that the blueAir has the smallest fan and the Sharp has the largest fan.

interesting assumption. The blueAir the largest one, by far.

and i wrote wrong! i don't have a sharp one. the silent one is from sanyo! it also has the ONLY truly silent humidifier included, though very low volume as it is only used for the ionizing shenanigans.

The site states RMB which stands for Ren Ming Bi, aka Yuan, aka PRC currency. It looks like a very specific market and I can see what they put together a DIY kit to drive the cost down given the market.

There is not 200 bucks of anything in it.

http://www.amazon.com/Shop-Fox-W1746-Fine-Filter/dp/B000QD7Y... is a good choice if you want a single large room done.

Hmm so I wonder if one should buy the carbon filters and tape it to the intake side. It's a cheap upgrade. A wire mesh in front of that might be good for the very large particles like hair or dust balls.

I have the same air filter and it works great. There wasn't anything by a reputable brand for less. So yes, there's a lot of valuable plastic and a quiet and reliable motor.

one reason might be that the market is much smaller for those then for fans or filters separately (smaller order quantities for the manufacturer = higher costs)

Below is the one I have and am very satisfied.


I'd like to rent one of those air quality testers for a week, anyone know where/if that's possible.

See http://iphone.bjair.info/

The air pollution ATM is at 366 PM 2.5 when this post was made. The chart now tops out at 300 with the hazardous description; the US embassy got rid of the crazy bad description given that the Chinese government wasn't so happy about that.

We went all the way up to 800 and 900 last January; we got up to 424 just last week. 0-50 is considered clean air, Salt Lake City institutes burn bans whenever their AQI goes above...35. There was a scandal when it got to 55 or so last year.

Hey, this is Thomas--I started Smart Air and the Particle Counting Tumblr that preceded it (http://particlecounting.tumblr.com/).

Thanks for all the useful suggestions! Our main philosophies are to (1) not rip people off and (2) be open about our data. I post data and testing methods to Particle Counting on a regular basis.

Simon--you're right about the fan speed. We've been doing experiments with more powerful fans, and we'll be coming out with a more powerful model soon. It'll be better for bigger spaces, and it cuts the particle counts down a lot faster. The fan is a bit more expensive though.

These 20x20x4 inch HEPA filters are much better than standard 1 inch a/c filters. They are the right size for putting on your box fan.


Shipping is free, and with the coupon code TWITTER10, you'll save some money.

For someone living in a city with reasonably clean air and no smog problem, does filtering the air in their living space provide any long-term health benefits?

This is Thomas--founder of Smart Air. Interesting question. I've seen plenty of studies showing the effects of air pollution on people's health (the study showing pollution shrinks fetus size is particularly scary: http://www.news.qut.edu.au/cgi-bin/WebObjects/News.woa/wa/go...)

But I haven't seen experiments done with home air filters using health effects as the DV. I'd actually love to donate some filters to anyone in public health or medicine who wants to run that study!

Negative ionic air purifiers may help with SAD (seasonal depression) [1] similar to daylight bulbs. Research is somewhat inconclusive.

It also supposedly makes air have equivalent ionic levels to "country or mountain air". Apparently in the city/offices the ion levels in the air are quite lower than in rural areas which is harmful. This of course is the sales pitch from the companies selling them.

But at the same time the filters kill bacteria and pet dander (which is always good).

I found a HEPA air filter that contained negative ionizer for around ~$50 on Amazon which I use in my home office.


Why is killing bacteria always good?

Ah the perils of text language. You're not sure if he's referring to both bacteria and pet dander or just pet dander.

Yes, it's somewhat ambiguous. You don't even know if they kill bacteria and they pet [verb] dander. English grammar is crazy ambiguous.

hah good catch, pretty crazy actually.

There is no "safe" threshold for particulate matter (PM) exposure. Our nose, mouth and throat are very inefficient at filtering particles less than 2.5 microns. As a consequence, a large proportion of these particles simply enter the respiratory tract (tracheobronchial and alveolar regions) relatively unimpeded.

Assessing indoor exposure to PM is challenging because it is highly dependent on location, the physical properties of the home, and human behaviour. Consequently, it can be difficult to clearly identify/quantify health benefits.

Even though you live in a reasonably clean city, you can still further reduce your exposure to indoor PM by changing your behaviour, filtering your air and using existing equipment in your home properly.

1) In non-smoking homes, the biggest indoor source of PM is cooking (especially frying and broiling). You can reduce your exposure by a) keeping your range hood in good working order (change filters), b) using the range hood every time your cook, c) opening a window while cooking and d)stepping away from the stove whenever possible.

2) There are multiple other sources products that can produce shocking amounts of PM through direct emission and secondary reactions involving ozone. I would describe these exposures as completely unnecessary and can be eliminated by simply not using the products in the first place: a) candles, b) incense, and c)air fresheners and cleaning products with lemon & pine scents.

i don't have a study, but i live in santiago, which has smog in winter, and buying an air filter cured (or at least coincided with the cure of) my bronchitis.

200 rmb is about £20, or $32, or €24

Errr - this is expensive for what you get. Among other things, the CFM is so low that it takes hours to reduce the particle rate any appreciable amount, as their own tests show.

You'd do a lot better with a standard high velocity fan (also 35 bucks, and you can get them cheaper): http://www.northerntool.com/shop/tools/product_200361823_200...

You want to be changing the air at a much higher rate than they are.

They quote a 13.5 square meter bedroom. This is 145.313 square feet. If they have 8 foot high ceilings, it's 1160 cubic feet.

In order to be changing the air so little as they are, my guess is this box fan is ~40CFM, giving ~30 minutes between air changes.

For 30 bucks, you can get a 2000+ CFM fan (see above), and put the filter on the intake side rather than the output side. This would change the air in the room roughly twice a minute, or roughly 60 times faster. There will be some loss of CFM due to static pressure increase, but ...

They also probably want a cheap, washable, electrostatic pre-filter so you aren't wasting the filtrating on easily caught particles. Otherwise, you are just going to go through this hepa filter really quickly.

This is Thomas--founder of Smart Air. Thanks for the ideas!

I totally agree--we've been doing tests with more powerful fans, and the results are great. We'll be coming out with a more powerful model soon. Of course, it's a bit more expensive to get a more powerful fan.

We've avoided using pre-filters because we don't want to cut down on air flow (and HEPAs aren't all that expensive), but we'll probably use a pre-filter on the more powerful model.

About where to put the filter, is there a reason to put it on the intake side? I've heard several people make that argument, but I've never heard a good justification for it.

There are a couple reasons to put it on the intake side:

1. Otherwise you are pulling dust particles directly into the fan bearings/etc (though it may be that you don't have a good enough seal for this to matter anyway). All this does is lower the life of the fan. This is one of the reasons you see filters on the intake side of an A/C or furnace - to protect the innards.

2. If a non-dust particle gets dropped into the fan, with the filter on the outtake side, it is likely to get propelled through the filter at high speed. With the filter on the intake side, this will never happen (since it would not hit the filter), and even dropping it near the rear of the filter is unlikely to cause damage.

(There are other reasons that would matter more if this was an enclosed ventilation system, but it isn't)

Note that without pre-filtering, i can't imagine these filters are really lasting that long without being cleaned. Are you measuring static pressure increase at all to see how long they last before needing to replaced?

HEPA filters are not usually meant to be sole filters and last a long time. They are just too fine and load too quickly. Some form of coarse separation (IE >5 micron particles) is usually necessary to get any real life out of them.

I haven't tried both, but it does seem like on the intake side, suction from the fan blowing would tend to hold the filter in place. But I would expect you would still need the strap (partly to keep it together when it isn't running).

I am actually looking for a solution where the filtering is done through water rather then a HEPA filter, which needs replacing quite a lot in a environment as bad as Bejing.

Use aquarium air stones. The smaller the bubbles and higher the column of water the better.

Wonder if a fully functioning fish take would be even better - if you get plenty of plants growing, they will feed off the water/each other in my experience. The rate of air injection would likely have to be higher than that of a normal fish tank though? I used to run a fish tank with CO2 injection to get the plants growing well. The best, cheap way of doing this was to put CO2 into the filter intake, that way big bubbles which escapes the diffuser were blended up by the impeller of the filtration.

AFAIK you could introduce mosses (Vesicularia and the likes) instead of higher plants, they're not as CO2 dependent. Every aquarium tutorial I ever read tells me that air pumps lower the CO2 content and you need injection as you explain.

Those require reasonably high pressure and push low volumes though?

A cheap air pump for an aquarium will produce enough pressure for a string of air stones. I have a 10$ pump (2W) on my desk here that blows 4 stones and I still have to limit the flow a bit or the display looks more violent than soothing. More expensive pumps not only have more power but will also have a better design with less noise.

I think that people in Beijing and other Asian or American countries should stand up more often and force their governments to install filters on each fabric's smoke pipe and charge those who don't comply with a big fine. You can then open a petition that votes for using the money generated from that fine to for deploying fuel-less car alternatives… Come on, tell me you're helpless and dependent on your government and that your voice is not worth anything, that you can't change your country.. If you agree sir, I'm sorry. Sorry that you're not standing up for your rights. But then dear citizen, have the courage and inhale the smog in all it's glory and purity.

The DIY Filter idea is great to have a transitional solution and I applaud the startup for this idea. But a government, a country, a company, or a stakeholder, none of them can make profit and money, when there are no trees to cut, no clean air to breathe, no healthy citizen to employ, no educated class to teach, no unpolluted earth for the seed and no will for change. Then you've created the perfect environment for a colony of sheep that follows a butcher who sells himself as a shepard.

Obviously the solution is for Beijing to clean up its act; literally. But it will take them awhile, and we need to worry about this now. As a foreigner in Beijing, I actually have no political rights, though I'm proud of the American embassy for reporting crazy bad pollution in the first place and getting the Chinese government to admit that there was a huge problem more quickly.

While I agree in general, one of the biggest sources (if not the biggest) of dust in Beijing's air is the desert Gobi. It will be pretty hard to build an appropriate filter. ;)

In my experience Beijing's air is really "special". Hot, humid, dusty. Not my favorite environment.

The dust is not as bad these days as 10 years ago; the tree planting in Inner Mongolia and hebei has worked surprisingly well. These days, pollution from artificial sources is a much bigger problem and we've mostly forgotten about dust, but sand storms still occur occasionally.

Axial fans, especially those for household purposes do not offer the required pressure drop of approx. 300 Pa (https://en.wikipedia.org/wiki/HEPA#Specifications). Axial fans have typically a high throughput but low max pressure difference (see eg. http://www.adrianagarcia.me/wp-content/themes/twentyeleven/a...). HEPA filters require radial (or centrifugal) fans for acceptable throughput.

As well, a HEPA filter becomes clogged very rapidly without appropriate prefilter. This means that the pressure drop required increases considerably definitely beyond reach of any household fan.

>Axial fans, especially those for household purposes do not offer the required pressure drop of approx. 300 Pa

It might fall short of the official specs, but its difficult to argue with their results.

What kind of prefilter would one need? I'm thinking of DIYing this...

>It might fall short of the official specs, but its difficult to argue with their results.

For this one would need to know the exact measurement setup. For real world performance it is important to know the approximate exchange rate of air of the room. The throughput of the fan across the filter must be considerably higher than that.

>What kind of prefilter would one need? I'm thinking of DIYing this...

First of all, you would need a radial fan to overcome the required pressure drop. As for the prefilter, I am from Europe, which has probably different standards than the US, but some overview is provided here: http://www.filtration-engineering.co.uk/air_filter_testing.h... . For my clean room set up I had a EU5 prefilter combined with a EU9 main filter. Afair, laminar flow boxes for dirty environment (i.e. not supposed to be used within a clean room) have EU5 (or the equivalent) prefilters as well.

Interesting. Why do you have a clean room if I may ask? I'm guessing data recovery?

I was in making photographic (those with silver halide) plates in the 90's. That's a wet chemistry process which does not tolerate any dirt in the final product. I made a good deal of the required machinery on my own so I have some basic knowledge on clean room design (albeit a bit rusty).

Nice! I had read something similar for a wood workshop here: http://woodgears.ca/dust/air_cleaner.html

Seems to be quite effective.

Also, if you're into woodworking, woodgears is probably one of the best, if not the best on the net.

I stumbled upon woodgears.ca after watching woodwork Youtube videos. This guy is so awesome.

Here is his 3D Pantograph:



Hopefully that's in addition to a dust collector https://www.google.com/search?q=dust+collector

Can't you just do this with a normal box fan and a hepa air filter you buy for 7usd at the market?

From the FAQ:

You can! We have links on our Particle Counting blog. We're more committed to spreading the knowledge that HEPA filters are a cheap way to effectively combat air pollution than we are to making money, so we'd never discourage anyone from buying the same parts elsewhere.

We just try to make the parts easier to get for people who don't want to scour Taobao for the cheapest filters. People have also emailed us saying that some stores stop carrying fans in the winter and that some HEPA manufacturers don’t sell in small orders. We buy in bulk so we can offer a low, flat rate (200RMB) that includes shipping anywhere in Mainland China. By buying with us, you also know that you’re getting HEPAs that we tested personally for effectiveness.

The irony is that running all of these filters is consuming electricity, which in turn means more coal-fired power plants and even dirtier air for everyone. Beijing should move to clean up the environment.

The irony's not very strong, since these can clean a lot more than they contribute via electricity consumption.

Yes. I've been doing this for years.

It is amazing how much the air flow is cut down by the filter, though.

Just ordered one, and also a Dylos DC1100 particle counter. I'm often in Shanghai, and pollution can get pretty rough even if we have it better than in Beijing. I'll make sure to measure the hell out of it and see if it really works. :)

Edit: I know the particle counter ($200) is 6 times the price of the air purifier, which can seem ridiculous; but to me it makes much more sense to do that than to buy a $300 air filter and just pray for the best while having no clue at all about what's really going on.

I like this product, it appeals to a market where there isn't much money to spend and is probably effective.

The consumer air purifier market is a mess. There is so much misinformation and fake reviews out there that it's impossible to make a decision.

Each company runs dozens of smear sites against everyone else. All the Amazon reviews look fake. All the companies seem to have something wrong with them. It got to the point that when I was doing me research I just gave up and decided to not buy anything.

Are particles the whole story when it comes to air pollution, or do you have to worry about gases, too?

Also, what would be a good source for obtaining HEPA or carbon filters in Canada/USA?

Hey, this is Thomas, founder of Smart Air.

Excellent question! Particulates are very important, but gases can be a problem too. We talk about gas pollution in our workshops, and I've written about it on Particle Counting:


However, I don't know of home filters that target gases.

There are various indoor plants that are said to help with indoor pollution.



TED presenter Kamal Meattle argues for: - Areca Palm - Mother-in-law's Tongue - Money Plant

Your guess that gases are also an issue is correct. For example, ground-level ozone and sulfur dioxide typically also have negative effects on the respiratory system. In the U.S., the Air Quality Index (AQI) is computed from five components: ground-level ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide. Of those, particulate matter is the one that's easy to do something about in a DIY fashion, since it can be filtered indoors with relatively low-tech filters. So it's worth doing if you live in an area with poor air quality, even if it's only a partial amelioration.

As far as I know, there is no practical way of filtering out the other AQI-component pollutants using consumer-level technology. It's possible to filter them: power plant chimneys have devices called "scrubbers" attached that filter out things like SO2 [1]. But I don't think there exists a device you can place in your living room that does so.

[1] http://en.wikipedia.org/wiki/Flue-gas_desulfurization

Or strap a $1 central A/C filter to a $10 box fan.

That is not going to filter out PM2.5. Those filters only exist to protect the internals of the A/C unit from large debris.

This is good, but why is it in English, not Chinese? If you want to reach people wouldn't the best way be to post on the various forums netizens like to hang out in?

Maybe they are trying to connect with the expat community.

The copy at the top seems a bit wordy to me.

How about this? http://i.imgur.com/whD4yWh.png

Crazy. I was just thinking about doing this in my place a few months ago. I was going to actually build a little container that fit in a window and have a HEPA filter from McMaster-Carr (or wherever) sitting behind computer tower cooling fans, as these fans are designed to be quiet and low-power. This design has a ready-made chassis, though.

You get a lot more flow with a squirrel-cage fan; I don't know a cheap source of those though.

I've used HEPA filters when I built an IV glove box a couple of years back. Don't recall the numbers, but I needed a fair bit of pressure from the air pump to get a decent flow rate. Somehow I don't think a fan will do it.

Did you even read the data that shows otherwise?

Did you even bother to look up basics of HEPA filters? They require an initial pressure drop of 300 Pa (https://en.wikipedia.org/wiki/HEPA#Specifications), which is beyond reach of any household fan. When the filter bcomes clogged, the pressure drop will increase even higher.

Updated: Grammar

This depresses me.

What about it depresses you?

The fact that people need air filters? Or something about the way these people are doing it?

I really like their website. They're open and honest about not being experts, and about how they do things, and how they want corrections and additional information. They sell you a kit if you want it, but they make no secret about it being really easy to do by yourself.

It's a classic case of negative externalities caused by stupid human decisions and a complete disregard for the commons. People have been shitting in the commons so long in Beijing that the particulates in the air are crazy high. Everyone feels like this have to have a car instead of pushing hard for effective public transportation. Since everyone has to have a car, it hurts everyone on buses because the traffic is so bad the busses can't get anywhere on time anymore[0]. Then everyone has a building that is heated by coal, instead of making an effort to upgrade the buildings to some form of heat that isn't going to dump thousands to millions of pounds of particulates into the atmosphere.

Instead of solving the problem at the root, everyone takes an every man for himself approach to the problem like the one described by the OP. The government should provide some sort of tax incentive to every building willing to upgrade their heating to something cleaner and should tax the hell out of cars in the city and put that money towards public transportation

FWIW, I lived in Beijing back in 2005/2006 and had a solid smoker's cough after a year. It's truly disgusting how everyone is effectively poisoning each other there.

[0] Furthermore, the design of the onramps and offramps on the ring roads are such that they cause a cascading locking condition once the level of traffic hits a certain point. When the line to exit a ring road gets long enough, it blocks the on ramp. This causes locking to cascade through the whole city.

Beijing is the victim of geography where pollution is often trapped in an inversion; a problem like Salt Lake City in the states. Beijing has much fewer cars per person than say Seattle, and the problems arise from too many people more than too many cars, coupled with shitty cheap oil refined poorly leads to a huge problem in aggregate. On the other hand, the subway system has been built up nicely, and is expanding very quickly, though it is always wicked full and not very comfortable by western standards. Beijing's traffic problems simply boil down to too many people and cars and not enough road with nowhere really to build more.

Old coal boilers are another problem, and a lot of pollution blows in from the Hebei country side and gets stuck in Beijing without an outlet. All buildings in Beijing are heated by the city, so it's not even the building owner's option to be more efficient. Beijing is slowly switching over to natural gas for heating but the transition will take a couple years to finish.

The AQI right now is down to 50 where it was 340 only a few hours ago. I can only imagine we got some wind to blow out the bad air all of a sudden.

Cool; for a couple of years now, I've purchased furnace filters and used a simple box fan. It handles a great deal of particulates in the air (compare rooms during a sunny day with an without the fan is very stark)

Pretty cool idea, but given that the target audience are people living in China, why is the site in English instead of Chinese? Is the target Americans or other English speaking people living in China?

First though: Why would I need this. Then I saw something about Bejing, where I believe there's lots of smog(?).

Would this help against lots of smog?

If you live in Beijing, you need an air filter. We were about to buy an expensive one, but this is quite nice; we might just go with it.

Yes, HEPA filters are effective against particulate air pollution in Beijing.

I love simple and affordable alternatives to otherwise expensive solutions like this. This is a fantastic idea.

Could have used this when I lived in Xi'an for a year. Coughed the majority of the time I was there.

here's a discussion on zhihu.com (in Chinese): http://www.zhihu.com/question/21951887

Guys at http://aaaiiirrr.com/ are doing the same thing, but Open source.

How is the OP's article not open source? They tell you exactly how to make it using parts bought from a local hardware store.

I don't see anything on their website. Looks like a new install of wordpress.

Sorry - it was http://aaaiiirrr.org/ not .com

That is true. I met guy on BarCamp in Shanghai. They are part of local hackerspace.

Why put the price in RMB?

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