Can you run an Air Purifier and a Humidifier at the same time?

Can you run an air purifier and a humidifier at the same time?

I did a quick Google search. Here are the first results that pop up (in a nutshell).

Google search results for the query “Can you run an air purifier and a humidifier at the same time?”:

  1. Yes (no explanation given at all) (source)
  2. Of course, now buy our filters (source)
  3. Yes… we are an industry leader in superior filter systems – contact us and buy from us! (source)

I can’t help but read these answers with a clown voice.

For whatever reason, this simple question is absolutely dominated by trash content put out by the air filter industry.

And, if you know my blog, I am sick of companies putting out content without substance trying to sell me their stuff.

Message to the air filter industry: It doesn’t work like this! Nobody buys your “superior” filters.

So, here’s me, Daniel, an electrical engineer. I am not affiliated with any company. On this website, my mission is to provide you with answers with substance and real-world advice.

I don’t want to sell you anything.

Today, we’re going to check whether running an air purifier and a humidifier at the same time makes sense.

And if yes, how to do it. (Yes, there is an ideal way to do it).

So, let’s jump into the depths of air purifiers and humidifiers and find out!

Quick answer: Yes, you can run an air purifier and a humidifier at the same time. However, place them far apart. Otherwise, the air purifier will pull in water droplets from the humidifier and accumulate moisture over time.

Does an air purifier filter absorb humidity?

The problem of running an air purifier and a humidifier simultaneously essentially boils down to a key question: Does an air purifier filter absorb humidity?

That’s the core question we’re having a look at.

Because, if air purifiers don’t absorb humidity, they don’t interact with humidifiers. Meaning neither device affects the other.

If, however, air purifiers absorb humidity, that would be a problem. You don’t want to add water to the dust, dirt, and bacteria on your purifier filter. This would turn the filter into a breeding ground for more bacteria.

So, let’s check:

Size of water molecules: Can a filter catch them?

In most places where the humidity levels are very low, it makes sense to run a humidifier. When the humidity levels are low, water evaporates easily.

Then, your air purifier encounters this evaporated water in its gaseous form: steam.

Steam is invisible and consists of water molecules bouncing around heavily. Steam does not contain droplets of water, so it’s invisible.

If there were droplets, we would call it vapor!

So, can an air purifier filter steam?

To answer that, we have to look at the size of a water molecule and at the HEPA standard. HEPA is the air filter standard most quality air purifiers follow.

A water molecule is tiny. Its size is just 0.275 nanometers! Because scientists don’t want to use fractional nanometer sizes for molecules, they invented a new size unit, specifically for particle physics, and called it “angstrom”.

1 nanometer = 10 angstrom

“The water molecule is composed of hydrogen and oxygen, in a ratio of two volumes of hydrogen for each volume of oxygen, with the molecular formula H2O and a molecular diameter of about 2.75 angstrom.”

ENLIST Chemistry Workshop, University of Illinois

Water molecules are, in fact, the smallest molecules in the universe.

Now, let’s check which size particles HEPA filters can collect:

“To qualify as HEPA, the filter must remove 99.97% of particles down to 0.3 microns from air that passes through it.”

This does NOT say a HEPA filter can’t collect particles smaller than 0.3µm! In fact, the smaller a particle is, the better it can be collected by a HEPA filter.

However, the filtration efficiency apparently decreases once you go below a certain size. 

Gas molecules (like water steam), are just a whole different size category on their own. They are so small, they just fly through HEPA filters without any obstructions.

And that’s a positive result for you!

Since water steam just passes through your air filter without interacting, a humidifier does not have any effect on your air purifier.

However (and here’s the main setback of this article):

Humidifiers do not emit steam! They emit water vapor.

Do air purifiers filter water vapor?

Water vapor is steam mixed with millions of tiny droplets of water. The droplets are what makes the vapor visible. Steam, in contrast, is invisible.

“Steam in general refers to the gas phase of water. Steam can be the same as water vapor in some contexts. In more casual usage, steam can refer to the mixture of vapor and aerosol liquid water droplets suspended in the vapor.”

JMac on

Humidifiers emit visible water vapor. The vapor contains tiny water droplets.

Depending on where you live, there are now two possible scenarios:

  • If you live in a dry place, the droplets in the water vapor will eventually vaporize and turn into steam.
  • However, in humid places, the air already has high water content. So, vapor might not fully turn into steam.

These droplets are large enough for a HEPA filter to catch.

The average diameter of a water droplet is 10 – 15 microns (source).

That’s about 30.000 to 60.000 times the diameter of a water molecule!

So, while HEPA filters can’t catch water molecules, they can easily catch water droplets. In fact, water droplets are so large that HEPA filters will likely catch 100% of them.

An air purifier will catch all water droplets passing through it.

That’s not good!

When water accumulates on your air filter, it becomes a breeding ground for bacteria and bad smells.

And on top of that, the air purifier even dehumidifies the air you’re trying to humidity by absorbing all the water droplets!

Intermediate result

In hot and dry air, air purifiers and humidifiers do not interact, since the humidifier’s water droplets vaporize to steam.

In cold and humid air, air purifiers will filter the water droplets your humidifier emits. This makes humidifying pointless and increases bacteria growth on the air filter.

One more note I have to add here

In humid air, where air purifiers and humidifiers would disturb each other, using a humidifier makes no sense anyways!

If you live in a humid place, you don’t need to run a humidifier.

In any (dry) place, where humidifiers make sense, it is no problem to combine them with an air purifier.

air purifier humidifier vapor
If too close together, your air purifier will pull in the vapor from your humidifier and absorb the water droplets. This effectively renders the humidifier useless and wears down the air purifier’s filter.

How to place an air purifier to use it together with your humidifier

As long as you live in a dry place, water vapor coming from the humidifier eventually transforms into steam.

However, this transformation takes a couple of seconds. Even in hot and dry places. You will always see water vapor coming from the humidifier initially.

While the water is in its vapor stage, it should not get near the air purifier, since the filter would catch all the moisture.

So, the key learning from this section is:

Never place an air purifier immediately next to a humidifier.

Ideally, both devices should be as far apart as possible to minimize the likelihood of water droplets entering your air purifier.

In the summertime, it doesn’t matter where exactly you place your humidifier and your air purifier. Just place them at opposite ends of your room.

In the wintertime, however, water droplets evaporate less easily (because it’s so cold). Therefore, place your humidifier near a heat source, such as a wood stove, a radiator, or similar.

The heater helps the water coming from the humidifier evaporate. And once the water droplets are evaporated, your air purifier can’t filter them anymore.

Most importantly, don’t place your humidifier in a cold corner of the room! In cold corners, even more, water vapor condenses into droplets, which in turn, makes evaporation even harder.

Do humidifiers spike an air purifier’s power consumption?

If you place your air purifier and your humidifier far apart, they don’t interact.

Also, humidifiers do not affect your air purifier’s power consumption.

The main power consumer in an air purifier is the built-in fan. Humidity does not affect the fan at all.

A humidifier can only affect an air purifier if you place both devices right next to each other and the air purifier sucks up all the humidity from the humidifier. Humidity in the air filter would increase air resistance and spike the air purifier fan’s power consumption.

For that to happen, however, you need to intentionally do everything contrary to what you learned in this article (e.g. run the purifier and humidifier right next to each other in a high-humidity and cold environment). 


No, a humidifier does not affect the air purifier’s power consumption.

Can humidifiers harm your air purifier’s electronics?

Similarly, a humidifier does not affect your air purifier’s built-in electronics, as long as you don’t intentionally run both devices right next to each other.

As long as there is some space (say >10 feet) between both devices, an air purifier can not absorb the humidity from the humidifier.

The increase in relative air humidity does not harm the humidifier. It’s just too little water to affect the electronics.

Also, air purifiers are very simple devices. In principle, it’s a simple circuit board connected to a fan. Both the fan and the circuit board are embedded deep inside the air purifier.

They don’t just fail on accident. You’d have to intentionally do something wrong.

For an electronic failure to happen, you would need to pour water over your air purifier.

Don’t try it!

No, a humidifier does not harm an air purifier’s electronics.


You can run an air purifier and a humidifier together as long as there is a distance between both devices.

As long as you don’t run your humidifier in an environment that’s already humid (even without the humidifier), there is very little that can go wrong.

Only if you place your air purifier and humidifier right next to each other, your air purifier will suck up all the water droplets and accumulate moisture.

This would be a stupid idea. At least after reading this article.

I hope I could help you.

Kudos: The guy explaining water vapor vs steam

It took me some time to really understand what water vapor is. Especially, because scientific terms about phases and critical temperatures are totally confusing.

And on top of that, the casual language understanding of steam and vapor differs.

In this article, I used the term vapor for gaseous water mixed with water droplets. And I used steam for purely gaseous water.

I based my understanding on this phenomenally simple video.

( Although I study thermodynamics at university, so I should know this without children’s science videos )

Thanks for explaining it, Mr. Wizard!