Is Xiaomi Mi Air Purifier 3H Auto Mode Effective? [Review]

Xiaomi air purifiers, such as the Xiaomi Mi 3H and 3C are some of the most popular air purifiers on the market. Many rely on Xiaomi’s auto mode to keep their homes clean. The problem? Our tests show the Xiaomi Mi 3H and other Xiaomi air purifier auto modes do not keep your air safe.

How Does the Xiaomi Air Purifier Auto Mode Work?

Xiaomi’s auto mode controls the air purifier according to PM2.5 levels. Once the sensor detects bad air it activates the filtration. As soon as the sensor notices cleaner air, the air purifier either turns off or reduces the fan speed.   

What’s Wrong with the Xiaomi Auto Mode?

Some years back we tested the auto mode functions of Xiaomi Mi 2 and Philips air purifiers. We found out they were not working well as they consist of cheap, inaccurate sensors and flawed technology. I wondered if technology has improved over time. That’s why I tested the auto mode of Xiaomi’s latest air purifier model 3H.

The Test: Xiaomi Mi 3H Auto Mode

The Xiaomi 3H is a strong air purifier with a CADR of 380 ug/m3. This means it can clean rooms up to 50-60 square meters. Since my living room is only 30 square meters, it should be an easy task for the Xiaomi. Knowing that the built-in PM2.5 detector is not trustworthy, I used my Kaiterra Laser Egg to measure the air quality. I put it some meters away from the air purifier to test whether the Xiaomi can purify the air in my entire room. 

Air pollution in Bangkok was pretty bad that night and ranged between 40 and 60 ug/m3 which is unhealthy. Yet, these are perfect conditions to check if the auto mode of the Xiaomi air purifier can do its job. I kept it running during the night while the Laser Egg was tracking the air quality. 

Result: Xiaomi Mi 3H Air Purifier Fails to Clean Air Properly

Checking the data the next morning, I saw the Xiaomi Mi 3H air purifier was never able to clean the air well. Although the auto mode reduced air pollution by 50%, it always left indoor air quality in the unsafe range. 

Xiaomi Mi 3H automode leaves air unhealthy

Hold On: Is Something Wrong With Xiaomi?

Skeptical readers may think, a 50% reduction is better than nothing. But according to WHO, 20 ug/m3 is still meaningfully bad air with serious health consequences. A reason why Xiaomi’s auto mode is not working as expected might be related to its loose definition of clean air. 

Xiaomi air purifiers follow the Chinese AQI which is more tolerant of air pollution than the US AQI. The Chinese standard, for example, classifies a PM2.5 concentration of 54 ug/m3 as good whereas the Air Visual App would let me know it’s unhealthy.

US vs. China AQI standard

This becomes tricky because most of the air quality trackers online use the stricter US AQI benchmark for measuring air pollution. But when one checks their Xiaomi air purifier, it will appear that the air quality inside is much better in comparison, since it uses the less stringent Chinese scale. 

The Chinese PM2.5 limit is 35 micrograms whereas the World Health Organization’s annual limit is 5 micrograms. Is 5 micrograms too low? I think not, because studies have found the risk of death from air pollution starts to increase significantly after 5 micrograms.

Open Data

As part of Smart Air’s open data pledge, our Xiaomi 3H test data is available for download.

Bottom Line: Xiaomi Mi 3H Air Purifier's Auto Mode Leaves Air Unsafe

The auto mode of Xiaomi air purifiers routinely leaves the air quality in the unsafe range. This is related to a poorly programmed auto mode and the different AQI standard it follows. The Xiaomi Mi 3H auto mode will not consistently give you clean air within the WHO safe limit, and users should be aware of this.

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