ASHRAE Recommended Air Changes Per Hour

Data shows that improving indoor ventilation can reduce the risk of virus transmission, and is recommended by the CDC. In this article, we’ll cover the ASHRAE recommended air changes per hour for offices, homes, schools, residential and hospitals, using the ASHRAE 62.1 and 62.2 guidelines. ASHRAE Recommended Air Changes Per … Read more

Blast in Hospital

Hospital Air Purifiers for COVID-19 [2021 Guide]

The demand for air purifiers in hospitals has surged due to COVID-19. Hospitals have turned to air purifiers to remove COVID-19 particles and the delta variant from the air. In this article, we tackle what you need to know about choosing an air purifier for a hospital setting.  Can Air … Read more

Blast Mini HEPA filter air purifier in office for protection against COVID coronavirus

Best PM2.5 Air Quality Monitors in 2021

PM2.5 air quality monitors can be a great tool to ensure the air you are breathing is safe. So what are the best PM2.5 air quality monitors in 2021? Which air quality monitors are the most accurate? PM2.5 Air Quality Monitor Tests The South Coast AQMD tested 55 PM2.5 air … Read more

Did Delhi's Air Quality Improve In 2020?

Did Delhi’s Air Quality Improve in 2020?

How was Delhi’s air quality in 2020? Did Delhi’s air quality improve in 2020 compared to recent years? For the previous three years, Delhi has seen little improvement in air quality. Air pollution levels have hovered around 10x the World Health Organization’s (WHO) recommended limit for PM2.5 levels. Smart Air … Read more

Can Activated Carbon Remove Formaldehyde?

Can activated carbon filters remove formaldehyde and VOCs? Earlier tests from Smart Air found that carbon can reduce VOCs from cigarette smoke. But formaldehyde and VOCs in general are particular concern for many people. We put activated carbon filters to the test by ordering formaldehyde straight from the factory and … Read more

Should I Run My Air Purifier All Day?

Some purifier companies recommend running your air purifier all day. But is that really necessary? If so, isn’t running the purifier all the time a big waste of your filters and energy?

Test Method

To get to the bottom of it, I set a Smart Air Cannon on a timer to turn on for two hours everyday in a 13.5m2 Beijing bedroom:

Smart Air Cannon DIY Air Purifier Filter

I put a particle counter in the room to take measurements every minute. I did the test while I was on vacation, so there was no influence of me opening and closing doors.

Results

After six days, I came back and saw how long it took to the Cannon to clean the air each time it came on. Here’s what six days of data looked like for the small .5 micron particles:

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Over the six test days, the air in Beijing became progressively worse. But on each day, it was clear when the Cannon turned on and off. The dropoffs were sharp, showing the Cannon was working quickly.

I averaged over the six test days to find out how long it took the Cannon to clean the air on average.

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Conclusion

On average, the Cannon cut 0.5 micron particulate in half in 10 minutes. By 20 minutes, it removed 80%.

Bottom line: Should I Run My Air Purifier All Day?Powerful purifiers like the Cannon clean the air very quickly, so I see no need to run the purifier while I’m not at home.

Can I turn it off while I sleep?

The data can also answer another question a few people have asked me: “I don’t want to hear the fan while I sleep, so can I run it for an hour and then turn it off while I sleep?

In the tests, the air got dirty very quickly after the Cannon turned off (even though the windows and doors were closed). Dirty air is entering our homes constantly, even though we can’t see it.

 

Purifier closed room air dirty again

 

Bottom line: I do NOT recommend turning the purifier off while you sleep.

Open Data

As always, I’m publishing the raw data and more details on the methods below. I’ll also be publishing data from similar tests in a much larger room (30.5m2) and for tests when I’m at home and moving in the room.

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How Effective Are Air Purifiers for Virus Protection?

Peer-reviewed scientific research has shown conclusively that HEPA air purifiers capture over 99% of viruses, even viruses as small as the coronavirus. However, it’s important to remember that air purifiers are not a silver bullet for virus protection. Things to Look Out For When Using a HEPA Purifier to Protect … Read more

Poor ventilation leads to increased virus transmission covid19 coronavirus offices schools

Poor Ventilation May Lead to Higher Virus Infection Rates

Offices and the workplace can be breeding grounds for viruses such as COVID-19. In this article, we’ll present data that shows how improving office ventilation and airflow may lower the spread of viruses like the coronavirus in the workplace. Evidence of how Office Ventilation Affects Disease and Virus Transmission There’s … Read more

Can Plants Filter Out PM2.5 Air Pollution From Our Homes?

Can plants be useful substitutes for air purifiers? Data shows that plants aren’t great at removing VOCs from the air. Despite a NASA study showing that some plants like ivy, spider plants, aloe vera and bamboo palm could reduce VOC levels, real-home data shows otherwise. But how well can plants … Read more

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.