Why Does My Humidifier Leave White Dust Everywhere?

Using a humidifier to boost the relative humidity of your home is great for your health and comfort when you live in a dry climate or just have very dry winters. But sometimes they can leave white dust on everything. What gives?

When it comes to home care the last thing anyone wants is more work, so we completely understand your frustration at the discovery that your humidifier seems to leave chalky white dust on everything. Here’s what you need to know about how humidifiers work and how to avoid that white dust coating your stuff.

How Humidifiers Work

Before we dig into the solution to the white dust problem, it’s important to understand how different styles of humidifiers work first.

Evaporative Humidifiers: If you have a whole-house humidifier attached to your forced-air furnace, you’re already familiar with evaporative humidifiers. They work just like the name implies. Air is passed over a “wicking” pad soaked in water. In turn that moisture evaporates off that pad and is carried into the air by a fan within the unit (or, in the case of your whole-house humidifier, by the blower fan in your furnace).

Free-standing evaporative humidifiers work by the same mechanism, they’re just not plumbed into your home’s water supply and you have to refill them manually. A wicking pad sits in the water and a fan blows air over it to help move it into your living space.

Vornado’s Evap40 is an example of a popular free-standing evaporative humidifier. (Though if you want something a little less institutional-looking and a little more stylish, you may want to get their EV200 model.)

Steam Humidifiers: A steam humidifier boils the water to release warm mist in the form of steam into the room. While there are some advanced whole-house humidifiers that use steam, it’s uncommon. Steam humidifiers are more common in stand-alone units.

Most of us are familiar with steam humidifiers, even if we don’t realize it, because of the ubiquitous little Vicks-brand steam humidifiers that have been on the market for ages—many a child has been soothed to sleep during a bad cold or bought of bronchitis thanks to those little steam humidifiers. There are bigger versions too, like the Vornado Element A.

Ultrasonic Humidifiers: Relatively new to the market, compared to evaporative and steam humidifiers, ultrasonic humidifiers raise the humidity of the room using a different mechanism. Rather than carrying the water into the air by evaporation or creating steam to let it drift away, ultrasonic humidifiers eject the water from the machine.

A little plate inside the machine vibrates at an extremely high ultrasonic frequency with such energy that it flings tiny droplets of water right out of the humidifier and into the air. The Pure Enrichment MistAire is a best-selling example of this particular design.

The distinct plume of “fog” that comes out of an ultrasonic humidifier has a certain charm (and is practically a staple in Instagram houseplant photography at this point). Using an ultrasonic humidifier is not without certain problems and pitfalls, however, so read on as we dig into the whole white dust issue.

Why Ultrasonic Humidifiers Leave White Dust

Now that we’ve taken a quick look at how each of the major types of humidifiers works, the question remains, why is it that only the ultrasonic dehumidifiers leave a layer of extremely fine white dust everywhere?

It all comes back to that high-energy delivery method we just talked about. When water evaporates naturally into the air, only the water enters the air. All the stuff in the water stays behind. That’s why when you sweat a lot and then dry off in the breeze your skin can feel gritty—the water left but the salt in your sweat stayed behind. Same thing with steam-based humidification. If you boil a pot of water long enough all the water is eventually gone in the form of steam, but the rust, calcium, and other junk in your tap water is left behind crusted to the bottom of the pot.

Ultrasonic humidifiers don’t convert the water to vapor, however. They just fling the water straight up in the air almost like it’s being shot into the room by microscopic squirt guns. This means all the impurities in the water travel right along with the water into the room.

That white dust on everything? It’s the minerals from the water you put into the ultrasonic humidifier. When you wipe your finger over your dresser and the dust seems white and chalkier than usual, that’s because it is. Instead of regular household dust, it’s regular household dust plus an incredibly fine layer of calcium and other mineral “chalk.” If you purchased an ultrasonic humidifier for your house plants you’ll likely find the dust on their leaves too.

On top of finding the dust settled on flat surfaces like the top of your dresser or coffee table, you’ll probably also notice that the dust coats vertical surfaces really well and is particularly attracted to electronics. Because it’s an ultrafine powder suspended in humid air, it’s more likely to stick to vertical surfaces and it’s very attracted to anything with a staticky surface charge like the body of your television or computer monitor.

Is The White Dust Harmful?

If you found this article by searching for answers about the mystery dust in your home, you might just have been motivated by the annoyance of dealing with the dust. But you may also have been curious if it’s harmful.

While you shouldn’t panic about the dust, you should also do everything you can to avoid it. Why? Because if you’re wiping lots of white fine dust off everything you’re also breathing in the same air saturated with the white “rock dust” minerals from your tap water (along with all the other impurities from the tap water that the ultrasonic humidifier is ejecting into the air along with the minerals).

No good ever comes from breathing in ultra-fine particulates and research conducted with mice indicates the particles from ultrasonic humidifiers pass deep into the lung tissue. Another study found that using a small ultrasonic humidifier in an upstairs bedroom raised the level of fine particulate matter in the air throughout the entire home as the air was circulated through the forced air heating system.

It’s certainly not as dangerous as grinding concrete without protective gear or working in an asbestos mine, of course, but if you can avoid putting unnecessary particulate into the air you’ll be better off for it.

How to Avoid the White Dust

Whether you want to avoid work of extra dusting or you’re worried about inhaling a mist of ultra-fine particulates, there are two simple solutions.

First, if you already own an ultrasonic humidifier or you just prefer using one (the plume of mist that comes out of them is pretty neat looking after all) you can continue to do so in a dust-free and safe manner by switching to distilled water.

Steam-distilled water is cheap and abundantly available at just about every grocery store. The water is free from impurities and when used in the ultrasonic humidifier it won’t leave white dust (or anything else) on your furniture or electronics. If you get tired of buying small jugs, by the way, you can often find distilled water in 5-gallon jugs from water delivery services.

Second, if you don’t want to deal with the expense and hassle of buying jug after jug of distilled water, you can skip that whole process by buying evaporative or steam-based humidifiers like the aforementioned Vornado EV200 or Vornado Element A. The only downside here is that you’ll need to clean the machine now and then with a mild acid like white vinegar to remove the minerals left behind during the evaporation process.

If you’re dealing with seriously dry winter air you may want to stick with evaporative humidification. Even though distilled water is cheap when you’re just buying a gallon here or there for your iron, it adds up fast when you’re trying to raise the humidity in your home. It’s easy to put a gallon or more of water into the air per day in dry climates. If you’re using tap water you might add a dollar at most to your water bill per month. If you’re using distilled water you’ll easily spend $30+ a month for the same increase in humidity.

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Whether you remove the minerals from the start (by using distilled water) or you use a method that keeps the minerals in the machine (evaporation or steam), though, you’ll avoid the white dust. Better yet, you’ll enjoy a more comfortable living space with less dust!