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.

dry climate air pollution

Do HEPA Filters Lower Humidity?

To test how turning on an air purifier affects humidity, we first burned cigarettes to pollute a sealed room…

Burning cigarettes to pollute room create air pollution

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

Smart Air Blast Mini air purifier and pet dog in office

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

Test setup to find if air purifiers with HEPA filters lower humidity inside

In 20 minutes, particulate pollution dropped from nearly 200 micrograms to zero (red line). But humidity did not drop at all (blue line).

Do Air Purifiers Dry Out The Air Humidity

Dry noses rejoice!

Do Carbon Filters Dry out the Air?

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

Sqair HEPA filter air purifier does not dry out air

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

Activated Charcoal Filter

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

difference between adsorb and absorb carbon filters making air dry

It seems plausible that activated carbon could adsorb water vapor too.

water molecules adsorbed by activated carbon filter to dry out air

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. Thomas and the Blast air purifier

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

Blast Air purifier large size activated carbon filter

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

air purifiers dry air humidity carbon filters

Thus, carbon seems to reduce humidity slightly. That makes sense with theory. Activated carbon is hydrophobic, meaning it does not attract water molecules. But activated carbon also has some oxygen in it, which attracts a little bit of water. When scientists tested it in the lab, they found that only a little bit of water vapor adsorbed onto the carbon.

Bottom Line: Do Air Purifiers Dry Out the Air?

HEPA air purifiers do not reduce humidity. Carbon filters slightly reduce humidity.

Smart Air

Caveat: if an air purifier or fan blows air directly onto your body, it can increase evaporation from your body and make you feel dry. There’s an obvious fix: point the air purifier another direction!

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

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