What Eats Airpocalypse For Breakfast and Doesn’t Cost Thousands of Dollars?

Four years ago, I was coughing through a Beijing winter and wanted some clean air. But all the purifiers I could find cost hundreds of dollars, so I strapped a filter to a fan I had at home and made my first DIY purifier.

Thomas First DIY Air Filter Setup


It wasn’t pretty, but I tested it with a laser particle counter, and the data showed it significantly reduced the particles in my bedroom air.

It worked, but it had some problems:

  1. It’s loud. On high, it’s about as loud as major purifiers, but that’s still loud.
  2. It’s kind of a hassle. You have to strap the filter on, and I’ve seen some people do it wrong.
  3. The fan isn’t really made to power through a dense HEPA filter. A stronger fan would give a lot more clean air.

Fast forward 4 years and hundreds of tests later, I’ve got a new pair of machines that squashes those problems, and they’re badass. They’re my first non-DIY purifiers. Meet the Blast and the Blast Mini (or Ladakh and Ladakh Mini in India!).


Meet the Blast and Blast Mini


OK, OK, the Blasts are pretty basic. It’s a metal box with a fan and a super fat HEPA filter inside. That’s not some kind of technological marvel. All purifiers are boxes with a fan and a filter inside, but the Blasts have a bigger fan and a much bigger HEPA. That means:

Blast Mini is equivalent to 2.2 BlueAirs

The Blast Mini puts out as much clean air as about 2.2 Blueair’s or IQAir’s.

Blast Mini and IQ Air Health Pro comparison

But with that much air coming out, it’s gotta be noisy, right? This bad boy is actually quieter than a Blueair or IQ Air.

Blast and Blast Mini Quieter than Blue Air IQ Air

As always, I’ve been testing this under real apartments and publishing all the data and methods. But it’s kind of unfair because they clean so fast. Here’s the Blast in the 34 m2 Smart Air office, and here’s a video of the test.

Blast Room test Beijing office


Throughout all this testing, several times I’ve asked, “Did anyone turn this on?” It’s that quiet. After experiencing it for a month, I bought up the first few to give to a few friends.

Your lie detector should be going off by now. How can it be more powerful and quieter? Well, for one, the HEPA is fat.

Blast Mini HEPA Size Comparison

(area calculated taking the HEPA filter and opening all the folds)


That means the air can spread out over a large area. Imagine trying to blow really hard through a straw. Now imagine blowing air through a traffic cone. It’s a lot easier, and it’s quieter.

Second, this guy here Paddy engineered the fan and air duct, and he’s an aeronautical engineer. Really. He believes in his creation so much he even pretended to read a magazine next to it.


Paddy designed the Blast and Blast Mini

It also means he knows how air moves and designed the fans so that they work well and stay quiet.

So the Blasts are more powerful and quieter, well then they must be more expensive. Nope:

Cost vs Effectiveness for Blast and Blast Mini air purifier

I calculated that the Blast Mini can easily clean up to 85 m2. That’s good for most apartments or houses. And for big apartments or places like offices, gyms, and cafes, there’s the Blast which cleans up to 130m2. And because the Blast’s HEPA is twice the size of the Blast Mini’s, it’s even quieter.


Blast purifier in situ in cafe


So, what makes the Blasts so special then? Not a whole lot, just in true Smart Air fashion I’ve packaged them without the high price tag and margin, and bundled them along with hundreds of hours of test data to verify they actually work.

My aim is still the same: make clean air more affordable, and get it out to more people.


As I write this, I want to apologize for feeling like I’m selling this thing. After four years of working on Smart Air, I still haven’t taken a penny for myself. I’ve got a day job (I’ve now moved from grad school life to professor life), so I use any leftovers to pay the Smart Air team an almost-livable wage, set up in India and Mongolia, and subsidize our educational workshops.

So I’m sounding a bit different from usual, but it’s because I’m excited. Four years after building my first DIY, the accumulated data is saying my initial hunch was right—it IS possible to get clean air for a heck of a lot less than what Blue Air and IQ Air say. Data sets us free!

Looking to get hold of a Blast or Blast Mini? In China, you can find them on our online store (English) or Taobao. For India, the Ladakh and Ladakh Mini are available from our India online store!

P.S. I couldn’t help making a GIF.

Blast Mini eats airpocalypse for Breakfast

Paddy profile pic

Paddy graduated in aeronautical engineering from Bristol University, and now runs Smart Air’s operations from Beijing. He’s an advocate for open data, free information and transparent business.

24 thoughts on “What Eats Airpocalypse For Breakfast and Doesn’t Cost Thousands of Dollars?

  1. Exciting! Would you kindly summarise from the data, a few points:
    – I see the noise level for the Blast and Mini on the loudest settings, but how loud are they at other settings?
    – What is the effective CADR at those other settings?


    1. We haven’t done CCM tests for the Blast and Blast Mini yet, but based on the total area of the Blast and Blast Mini HEPAs (22sqm or 11sqm) the CCM is most likely to fall into the P4 range (highest). We want to start doing longevity tests to determine this!

  2. Any chance of adding at least one similarly priced air filter (¥1500-2000) to your comparisons? The newish Blue Pure 211+ and Phillips 1000 Series are popular units targeting the same segment as the Blast Mini so either would both work.

    I’ve had great luck with my Cannon DIY and am excited to see you expand your product lineup. Keep up the good work!

    1. For sure Aaron, we’re actually in the process of comparing the Blast and Blast Mini to more similarly priced purifiers. What we’ve found is that they’re still far more powerful and more importantly much quieter. We’ll have the data out soon!

  3. Interesting that you talk about surface area. Could we get the same effect by running more than one DIY? Maybe one in each corner of the room. I would love to buy a Blast but live in Thailand so I imagine the postage costs would be high.

  4. Love your DIY filters, used both types in different places I lived in China. These are awesome products at awesome prices. Hope you can get some market penetration with this and start earning yourself a salary!

    1. Thanks Alex, always great to hear people are using Smart Airs to get clean air! Figuring out how to spread the word on the Blasts is now one of our biggest challenges, fingers crossed!

    1. We had the Blasts tested by a 3rd party testing lab, they tested for O3 (post is in Chinese). Here’s what they found:


      Put simply, the purifiers are not giving off any O3 (as we would make sure before creating any new purifier!)

    1. Hi Jian-Hong! Paddy here in Beijing. The motors we’re using are currently 240V only, but if you’re looking to order a larger quantity of units (more than 20) we can make sure they include 110V motors that work in Taiwan. Get in touch with us at info@smartairfilters.com if you do

  5. Hey, respect for your personal story, and obviously an awesome product development!
    I’m smoking, that’s why I want to buy one of that air purifiers…
    I also thought about an DIY project, and design my own, by this way I found your website…
    Can you send me some price infos, and shipping in the EU, Vienna, Austria, please?
    Wish you all the best, kind regards,


  6. Hi.

    For years I’ve been using 3M Filtrete cut out sheets on my air conditioners and on the backs of electric fans. Saw a Blueair 205 on sale recently, got interested, and decided to research more on air purifiers. Came upon your site. Great products!

    However there are some important errors you made in the comparison calculations. It appears that you compared the Blast Mini and Blast CADR using **cubic-meters-per-hour** (585 and 890 m³/hr) to the Blueair 203 and IQ Air Health Pro 250 using **cubic-feet-per-minute** (155 and 259 cfm respectively, according to their websites).

    So instead of the Blast Mini being equivalent to 3.8 Blueair 203’s, it should only be 2.2 (585/263=2.2). And instead of 2.2 IQ Air 250’s, it’s only 1.3 (585/440=1.3). I’m sure it was an honest oversight, but I suggest you change the marketing materials and documentation for this. I know it’s a lot but best to be correct.

    Also, I couldn’t figure out how the 85 m² (Blast Mini) and 130 m² (Blast) areas were computed. Based on the AHAM recommendations of 8′ ceiling, the Blast Mini is good for 50 m², and Blast for 75 m². I think it’s another volume/time unit conversion issue. They’re both 1.7x less than your published areas, which coincides to 1.7 m³/hr = 1 cfm.

    Is there an actual standard that most manufacturers follow to compute for effective area?

    1. Hi Sam, great insights! You’ve sure done some good digging work! The CADR values we got for the Blue Air came from the AHAM official website, double checking it again, it seems there’s a bug with their website whereby if you change the ‘units’ to ‘metric’ it still outputs the CADR of the BlueAir 203 as ‘155’. Having checked the BlueAir official website, you’re right: the CADR is 155cfm or 263cbm/hr! IQAir value is a little bit more difficult to decipher. IQAir doesn’t seem to give any CADR values (either in cfm or cbm/hr) for their machines, so in order to get an estimate for the CADR, we took the stated ‘airflow rating’ from their official website (in Chinese), and multiplied this by 0.6 (air purifier manufacturers and our tests have shown that CADR roughly equals 0.6 x airflow). I’ve updated the graphics and information to state that the Blast Mini is equivalent to 2.2 BlueAirs (and IQAirs – unchanged) and the Blast is equivalent to 3.4 Blue Airs. Thanks for pointing this out!

      Regarding your question what standard manufacturers use to compute effective airflow, there are typically two standards followed. The AHAM standard which can be found here and gives the formula Roomsize (sqft) = CADR (cfm) * 1.55 (this is the one you refer to)

      The other more common standard now in China is to use the formula taken from the National Standard GB/T 18801-2015, it’s all in Chinese, but if you scroll to page 24 you’ll see the formula S = (0.07 ~ 0.12)Q. This is saying Roomsize = between (0.07 x CADR) and (0.12 x CADR). We used this as a basis for our areas and then extrapolated based on the real world tests we’ve done in Beijing. So Blast Mini area from the Chinese standard = 585 * 0.12 = 71sqm, which we’ve found to be 10-20% conservative so rounded to 85sqm. The same is true for the Blast: area = 890 * 0.12 = 107sqm, for which we’ve found to be 10-20% conservative. Some explanations for why our tests show different from this could be that: 1) the room heights we normally see are slightly less than 2.4m (which is used in the Chinese standard), 2) most of our tests were done on days when pollution levels were <200µg/m3, the Chinese standard is based on 300µg/m3 (which typically only occurs 3-5 days a year somewhere like Beijing) and 3) that despite most people thinking to the contrary, most houses we've seen in China are reasonably well sealed, so air leakage isn't a huge problem.

      At Smart Air, we try and find a good balance between these 'official' numbers and what people will see in reality (all of which we back up with data), this way we hope to provide information that's more meaningful and relevant to people. If we can help stop people from overbuying and overspending on air purifiers, whilst still making sure people are breathing clean air, we'll do so!

  7. I think comparing the product to Blue Air is not relevant anymore as companies such as Xiaomi and Mijia makes it more affordable now, and have a pretty accurate automatic mode which is more friendly than these pick up devices for industrial use (and which i would not guarantee how safe their components are are they must be for domestic market)

    1. You’re right Flax! Many new purifiers have come on the market in the past few years which as you say have a much lower price. The Xiaomi purifiers are a good example of lower cost purifiers on the market! Although one of biggest downsides of the Xiaomi – which we spent a long time fine tuning for the Blasts – is the noise level. The Xiaomi gives a CADR of 310cbm/hr, but at a whopping 69dB. That’s pretty unbearable for most people. The Blast Mini on its lowest setting gives a CADR of 340cbm/hr, at a noise level of just 44dB. We’ve tested the Xiaomi in the past, you can read up on the Mi 2 here!

    1. Thanks John, sounds like a great idea! We already have the Blasts on Amazon India (they’re called the Ladakh and Ladakh Mini there). Which country are you based in and where would you like to see the Blasts for sale?

      1. I am based in South Africa and my audience is mostly American and European, and I do get some Indian visitors as well. I will see how I can work with your Indian amazon links for now but Amazon links for the U.S and E.U will be awesome. Thanks for reaching out

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