Improving the QT3 Portable Air Purifier for COVID-19 Protection

When we initially designed the QT3, we aimed to create a portable air purifier with the highest clean air delivery rate (CADR), while doubling it up as a fan. But after listening to our users and thinking more about the best test for a portable air purifier, we decided to make a design improvement.

QT3 design
3-in-1 design – portable, clean filtered air

A Gap or No Gap?

Here’s the problem: The QT3 filter holder leaves small gaps around the sides of the filters. Why are they there? Multiple third-party tests showed that keeping a small space between the filter and the side wall actually increased the amount of air cleaned (CADR).

Although some people understandably are skeptical of what companies say, fellow clean air nerds recognized that test results don’t always fit with our intuitions!

Smart Air QT3

For example, one theory to explain the room test (CADR) results is that the extra air flow around the sides helps mix the clean air around the room. Without the extra air flow, it’s possible that more clean air will stay around the purifier and not mix in the room as well.

Different Use Case, Different Test

But maybe CADR room tests are not the best test for the QT3. The CADR room tests measure how most people use air purifiers: cleaning air in a room.

But most people do not use the QT3 to clean a room. Instead, most people use the QT3 to create a stream of cleaner air in a larger room. That can be to reduce exposure to virus particles in the air or to reduce exposure to air pollution particles in polluted cities or places suffering from wildfire smoke.

If people are using the QT3 to get a clean stream of air, then the “clean air stream” test should guide our design decisions. Here’s what the clean air stream test setup looks like:

QT3 Portable Air Purifier Clean Air Stream Test Setup

We Listened to Fellow Air-Breathers on Twitter

A fellow clean air nerd on Twitter @CleanAirStars tried taping up the sides of the filters and running a “clean air stream” test like ours above. His results showed that taping up the sides produced a cleaner stream of air than leaving them untaped.

@CleanAirStars “clean air stream” test of the QT3 taped vs. un-taped

We pride ourselves on backing up all of our purifiers with open data, so we tried replicating Clean Air Stars’s tests. The data backed him up! Blocking up the sides (green line) produced a cleaner stream of air than without the side guards (red line).

At 50 centimeters, the QT3 reduced 0.3-micron particles 43.1% with side guards and 25.3% without the side guards.

Next we looked at larger 1-micron particles. The side guards also improved performance for larger 1-micron particles, although the difference was smaller.

After seeing the results, we are now shipping side guards with the QT3. Already bought a QT3? Contact the distributor you purchased from and request free side strips. It often helps to include the order number.

Smart Air QT3

Thanks to our fellow clean air nerds for the feedback and the encouragement!

Smart Air QT3
Smart Air QT3

The QT3 Portable Air Purifier Just Got Personal!

This video explains how to clip the side guards into the QT3. It’s simple!

Want portable clean air wherever you go?

Checkout the light, travel-friendly QT3, now available worldwide.


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Smart Air is a social enterprise that creates simple, no-nonsense air purifiers and provides free education to protect people’s health from the effects of air pollution. We are proud to be the only certified B-Corp dedicated to fighting air pollution.

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