For as ubiquitous as they are, humidifiers seem to be just one of those household appliances you tend to look past. They're just kinda there; a part of the house that seems as easy to ignore as a lamp or a washing machine.

But humidifiers deserve a closer look. Sure, they might seem like a one-function appliance, but their benefits go way beyond just moisturizing the air in a room. Did you know they can also keep your lips from chapping in the winter? Or that they help any ferns and ficus in your place thrive in cold weather? They can.

All this begs questions: What is a humidifier in the first place? What does a humidifier do? How do you pick out the best one for your home? Our handy guide is here to give you the basics on what to look for when shopping.

What does a humidifier do?

No matter the type, all air humidifiers do the same basic thing: they vaporize water before emitting it into whatever room(s) they are in. They pull this off in a number of ways, depending on the type of humidifier:

• Ultrasonic humidifiers use high-frequency sound waves to generate mist, and they use demineralization cartridges rather than filters.

• Evaporative humidifiers pull water through a wick (which removes impurities in the water) and expel it with a fan.

• Impeller humidifiers disperse water droplets via a spinning disc, which won't remove any impurities from the water.

What type of humidifier should you get?

Largely, this decision depends on two factors: the kind of mist you want (cool or warm) and the size of the room you're humidifying.

Cool Mist vs. Warm Mist

As their name gives away, cool-mist humidifiers don't contain any sort of heating element. Because of this, they're more energy efficient, they're a little better at humidifying larger spaces, and they may very slightly cool a room's overall temperature.

Warm-mist humidifiers heat their water into steam before releasing it. Many people prefer this type of humidifier since its heating element can kill germs in its water. Warm mist is also great for relieving sinus problems.

Room Size

Once you've determined the kind of mist you want from your humidifier, you'll want to take room size into account to find the model best suited to wherever you'll end up placing it.

• For small rooms (up to 300 or 400 square feet), go for a tabletop humidifier. They typically plug directly into the wall, they're portable, and their water tanks are easy to refill. Our pick: HealthSmart Mist XP ultrasonic cool-mist humidifier for $22.99.

• For medium-sized rooms (400 to 1,000 square feet), a tower humidifier is a good pick. They're still easy to set up, and they sport larger tanks than tabletop models, so they can last longer between refills. Our pick: Lifesmart 4-in-1 cooler, humidifier, heater, and fan tower for $117.99.

• For large rooms or multiple rooms (1,000+ square feet), console humidifiers are your best bet. Of the humidifier models that can be moved from room to room, they're as powerful as any you'll find. Our pick: AIRCARE evaporative humidifier console with adjustable humidistat and refill and filter-check indicators for $199.99.

• For entire homes, you'll need to call in the pros. A technician can install a humidifier into your home's ductwork to send moisturized air into every room. Browse HVAC and electrical service deals near you to find one.