Do Air Purifiers Dry Out the Air?

Empirical data shows that air purifiers are great at cleaning air, but do they dry out the air and lead to other health problems? For me, dry air is mostly just a comfort issue. But for some people, dry air can exacerbate health problems like allergies and bronchitis.

Do HEPA Filters Lower Humidity?

To test how turning on an air purifier affects humidity, we first polluted a sealed room by burning cigarettes…

Then we turned on the Blast Mini HEPA air purifier for 25 minutes.

During the test, we used the AirVisual Pro laser particle counter to track particulate pollution and humidity.

In 20 minutes, particulate pollution dropped from nearly 200 micrograms to zero (red line). But meanwhile, there was virtually no change in humidity (blue line). Dry noses rejoice!

Do Carbon Filters Dry out the Air?

But that was just a simple HEPA purifier—a fan and a HEPA filter.

Things get a little bit more complicated if we add a carbon filter. Carbon filters remove gas pollutants like formaldehyde, VOCs, NO2, and ozone.

Why is it more complicated? Carbon adsorbs these gases onto the surface of the carbon.

It seems plausible that water vapor could be adsorbed on to activated carbon as well.

But hey, lots of things are plausible! So we tested it.

We used the Blast because it has a massive carbon filter. The Blast’s carbon filter packs in a whopping 1.1 kilograms of activated carbon.

With such a large carbon filter, we can detect even a small effect on humidity.

The Blast did a quick job of cutting the pollution in the room. The Blast cut particulate from 250 micrograms to nearly zero in 15 minutes. Meanwhile, humidity dropped 2% in about 20 minutes.

That makes sense with theory. Activated carbon is hydrophobic, meaning it does not attract water molecules. When scientists tested it in the lab, they found that very little water vapor adsorbed onto the carbon.

 

 

Caveat: if an air purifier or fan blows air directly onto your body, it may lead to increased evaporation from your body and then a feeling of dryness. There’s an obvious fix: pointing the air purifier another direction.

---