Humidifiers vs. Dehumidifiers: How they work and what you need

It’s so humid. It’s so dry. Chances are, you’ve said one of those things to yourself (and recently), which is why you’re interested in humidifiers and/or dehumidifiers. If your home’s exterior is either muggy or arid, you may also be curious about what you need to better equip the inside of your home to compensate. Here, we’ll look at the differences between humidifiers and dehumidifiers, when to choose one or the other, what type works best in what circumstances, and if you even need one in the first place.

Humidifiers vs. dehumidifiers: The big (and small) differences

On the surface, figuring out the difference between an air humidifier and a dehumidifier for house and what they do is not difficult: Humidifier benefits include adding moisture to the local environment, and dehumidifier purposes include removing it, but the machines aren’t complete opposites. Here’s how to approach each one:

Humidifiers dispense water

Humidifiers need a tank filled with water to dispense in your home, though some advanced ones could use a hose feed. There are several mechanisms for taking the water and dispersing it into the air as vapor (we go through a few below), but they all function to work faster and “better” than evaporation.

Note that humidifiers can dispense things other than liquids. It is not uncommon for humidifiers to also be advertised as aromatherapy machines for dispensing essential oils.

Dehumidifiers accumulate water

The process of dehumidifying can essentially be broken down into four key steps:

1. Moist air is drawn into the machine and cooled.
2. The cooled air’s moisture begins to condensate out, like water on the outside of a glass of ice water.
3. This water is collected by a reservoir or pumped out.
4. The drier air is reheated and released back into the room.

Water storage or disposal becomes important. Nearly all dehumidifiers have tanks that accumulate the water being output. Many also have the option to include a feed or some sort of tubing that will drip the removed water into a drain or sink.

Humidifiers vs. dehumidifiers design considerations

Based on these differences, there are quite a few things that you can expect to be different (or desire to be different) from your humidifier to your dehumidifier. Here are just a few:

Automatic shut-off: One of the most common features of humidifiers or dehumidifiers is the automatic shut-off feature, or something similarly named. In dehumidifiers, this will usually trigger when the water tank gets filled to a certain level, should you be using it. Humidifiers will typically trigger their automatic shut-off when their tank empties. Both dehumidifiers and humidifiers may also have a shut-off associated with a certain achieved humidity level (via a humidistat), but you are more likely to want this feature on a humidifier due to the damaging effects of having too much humidity in a home.

Water tanks: The water tanks of humidifiers and dehumidifiers serve incredibly different purposes and, as such, you should expect differences from their designs. Since humidifiers need to be filled, you can expect a smooth internal water tank in an easy-to-reach location. Dehumidifiers, on the other hand, will often need to be dumped manually. This means that the water tank should be able to be removed, have at least one sturdy handle, and potentially have wave breakers.

Filtration and cleanliness: While you won’t want either your humidifier or your dehumidifier to get dirty, cleanliness is much more important when it comes to humidifiers. As we’ve collectively learned from COVID-19, tiny water droplets with bacteria and other toxins in them can cause serious conditions. For this reason, EPA humidifier health guidance recommends using distilled water, especially in ultrasonic and impeller humidifiers. Look for easy-to-clean humidifiers with built-in filtration systems. Note that many humidifiers are advertised as being BPA-free. In addition, some air purifiers double as humidifiers—and it’s a great combo because you can’t expect your houseplants to do all the work when it comes to air quality (though they can help).

Loudness, strengths, and scheduling: Operating machinery makes noise. Sometimes that noise is acceptable and others it is not. For example, a very powerful humidifier or dehumidifier might be so loud that you cannot sleep or hold a conversation properly. For this reason, many of these devices will have varying strength settings and even scheduling. While you might schedule a dehumidifier to turn off at night, if you need a humidifier for nighttime comfort, you may wish to seek one that includes a nighttime mode.

So, which one do you need?

The simple advice is that if your air is humid, you need a dehumidifier; if it is too dry, you should use a humidifier. In reality, it isn’t super easy to tell, so here’s how to decide if you need a humidifier or dehumidifier.

With low humidity, you’re likely to feel the effects directly. According to the Mayo Clinic, health conditions associated with low humidity include itchy eyes and dry skin—not exactly things that will kill you, but not comfortable either.

On the other hand, a dehumidifier might be better for you if your home shows signs of high humidity. While common concerns, like outgrowths of mold or even peeling paint, might prompt you to tackle your home’s humidity problem, they might not be the most obvious. One easily spotted but often misdiagnosed sign of humidity is winter window condensation.

If you’re still unsure about what you need in your home, consider getting a hygrometer. This is especially true if you have some, but not all, humidity or dry air problems … or a mixture of dry air and humidity issues. Effective hygrometers are much cheaper than humidifiers or dehumidifiers, after all, and a reliable hygrometer should run you under $10. 

Still interested in something larger? Continue reading for the different types and top picks when it comes to humidifiers and dehumidifiers.

Types of humidifiers

There are actually a ton of different types of humidifiers when you think about them at a mechanical level. Though there is occasionally a bit of overlap between one category and the next (many manufacturers use “cool mist” and “warm mist” very loosely), the following types of humidifiers represent the most commonly found types:

Ultrasonic: This type of humidifier uses intense vibrations to sort of “rattle” water into a mist or fog. Despite how it sounds, these humidifiers can be quite quiet due to their use of ultrasonic soundwaves.

Evaporative: Oddly enough, evaporative humidifiers use much of the same tech as wick-based hydroponics systems. Essentially, a wick is dipped in water, which then rises. The water is then dispersed into the air, possibly by a fan. As this process is a somewhat gentle way to get water into the air, it is easy to find examples of mist-free humidifiers in this category, as you are unlikely to see a visible trail of mist.

Impeller: Also known as “cool mist” humidifiers, these humidifiers use quick rotating discs to create a mist in the air.

Vaporizer: Also known as “warm mist” humidifiers, these humidifiers use heat to produce steam. Think of a device not unlike a kettle but more focused on the steam coming out of the spout than the water inside.

You can also think of humidifiers coming in two broad categories of form factor: central humidifiers and portable humidifiers. A central humidifier system is, much like central heating and air, a part of your home’s overall air “changing” system. They are whole-house humidifiers. Chances are, if you’re looking to buy a humidifier, you want a portable humidifier.

Since most humidifiers that you will encounter while shopping online are portable humidifiers, most will not explicitly label themselves as such, and if they do, it is likely to have the meaning that the humidifier in question is quite tiny or has a handle. In other words, it won’t be beneficial to search for a portable humidifier explicitly.

Types of dehumidifiers

Dehumidifiers are less robust in their design philosophy. Instead, use cases and form factors are where dehumidifiers will see the greatest variety.

For example, small dehumidifiers are pretty great for small rooms and bedrooms. Their low profile and (usually) lower sound output make them great for your room. However, more heavy-duty humidifiers, like these dehumidifiers for basements, are needed for more intense jobs. These more heavy-duty dehumidifiers are also the ones more likely to come with pumps that can be fed into your sink or bathtub.

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