Oct
If you want to keep your exposure to PM2.5 to the bare minimum, it’s important to know how the Clean Air Delivery Rate (CADR) of your air purifiers can affect the amount of particulate matter (PM) indoors.
In this blog post, we take a look at how the CADR of an air purifier (or multiple air purifiers) affects the level of PM2.5 in an indoor space.
What is Clean Air Delivery Rate (CADR)?
CADR is a value that signifies the amount of air that an air purifier (or multiple air purifiers) can clean in a room. In most countries around the world including Singapore, the CADR of an air purifier is usually signified in cubic meters per hour, or m³/h.
The higher the CADR, the more air the air purifier cleans in an hour.
It is important to note that by default, every air purifier company in the world lists the CADR of their air purifiers at top speed. Given that most people do not use their air purifier(s) at top speed all the time, you should consider what the CADR and noise level at medium and low is for the air purifier you’re considering to buy. A noisy air purifier is likely to be turned off, making it unable to clean the air.
For air purifiers with no data on their CADR at medium and low speed, their CADR at medium speed could be estimated by multiplying the CADR at top speed by 50% to 60%, and at low speed by multiplying the CADR at top speed by 10 to 20%.
Using a weak air purifier at low speed or sleep mode is like trying to empty a large swimming pool with a small tea spoon.
What is PM2.5?
PM2.5 refers to particulate matter in the air that are generally 2.5 micrometers or smaller. They could come in different forms, such as haze, pollen, traffic, industrial exhaust, and tobacco smoke. These tiny particles are invisible to the naked eye. After inhaling PM2.5, these particles can travel around your body through your bloodstream, potentially causing damage to your organs.
While the WHO (World Health Organization) recommends people to keep their exposure to PM2.5 to 15 ug/m³ over 24 hours and 5 ug/m³ over 1 hour, there is no such thing as a “safe limit” for PM2.5. This means that the less PM2.5 you breathe in, the less impact it will have on your health.
We have a comprehensive blog post on the harmful effects of PM2.5, which you can find here.
How does CADR affect PM2.5 levels?
The Clean Air Delivery Rate of one or multiple air purifiers can greatly affect the amount of PM2.5 in an indoor space. We demonstrate this with our air quality measurements on October 14, 2026.
On October 14, 2026, PM2.5 levels reached 360 ug/m³ outside the building of the dokuki office, and inside the building of the dokuki office, it reached 185 ug/m³. This was an unprecedented amount of PM2.5 that we’ve ever measured indoors, and the ventilation system was clearly struggling in removing the haze as we even saw smoke coming out of the HVAC air ducts.
In the dokuki office, we usually have two AirFanta room air purifiers delivering 1,418 m³/h of clean air at top speed, equivalent to 7.27 air changes per hour (slightly higher than our 6 air changes per hour recommendation for homes and businesses) in our office space.
While this configuration has worked well for us in normal times and for most of the haze season in limiting the amount of PM2.5 in our office (usually in the single digits), it was clearly not enough for the unprecedented amount of haze that day. During the haze spike, the PM2.5 levels inside the office hovered between 65 ug/m³ and 71 ug/m³, 63% lower the rest of the building.
After adding an additional AirFanta room air purifier at top speed, the PM2.5 level was reduced to 15 ug/m³ (92% lower than the rest of the building). While it’s higher than the single digit values that we usually see, it was certainly much better than smoking the equivalent of 3 cigarettes a day.
With the additional air purifier, the total CADR in the room increased to 2,120 m³/h, equivalent to 10.87 air changes per hour.
Conclusion
The results show the importance of using air purifiers with high CADR, as well as using multiple air purifiers in big spaces. It’s also not hard to imagine that in spaces with underpowered, undersized, or even no air purifiers, the amount of PM2.5 would have been much worse.
Upgrade your indoor air quality with AirFanta’s room air purifiers
AirFanta room air purifiers deliver up to three times more clean air than major brands in the same price range, allowing you to enjoy more clean air, breathe less PM2.5, and lead a healthier life.
Purchase AirFanta room air purifiers on dokuki.com:
Room Air Purifier
Room Air Purifier
