10 Things to Consider When Choosing a Room Humidifier

Humidifier steam
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A room humidifier is the best solution to moisten dry air in your home, especially if you don't have a whole-house, central humidifier installed in your forced-air furnace. Moistened air can help prevent or minimize a variety of respiratory health issues. Humidified air can help prevent dry sinuses, bloody noses, and cracked lips, and it can also help the symptoms of colds, bronchitis, and other respiratory problems.

But used incorrectly, humidified air can create its own set of health problems by breeding mold and bacteria. Therefore it's crucial to understand the features of various types of room humidifiers to buy one that's appropriate for your needs.

Operating Design

Your first choice will be to decide on the basic operating design of your humidifier. Room humidifiers come in four basic styles, each with a different mechanical method of increasing air humidity:

  • Evaporative humidifiers use a motor-driven fan to blow air through a wet wick, filter, or belt to evaporate water and send the moisture out into the room. The mist produced is cool, but these units require regular cleaning since they can foster the growth of mold and bacteria. They run fairly quietly and are relatively inexpensive.
  • Impeller humidifiers use a motor-driven rotating disc that flings water onto a diffuser, which then breaks it up into tiny droplets that float into the air. These cool-mist humidifiers may be a bit noisy to some people.
  • Ultrasonic humidifiers produce a cool mist using two ceramic plates that vibrate at an ultrasonic frequency. These are very effective appliances, but they can send fine dust into the air to settle on surfaces and may exaggerate allergy problems in some people.
  • Steam vaporizers use electricity to turn water into steam vapor that is absorbed into the air of a room. The moisture sent into the air is very clean, but avoid this type of humidifier if you have children or pets who may be burned if the humidifier is knocked over.

Cool Mist vs. Warm Mist

Your choice of humidifier design may be based on whether you prefer warm mist or cool mist. At one time, warm mist steam humidifiers were the most popular, and they still have advantages since the superheating of water is guaranteed to kill off any mold spores or bacteria before the moisture enters the air. Additional benefits of a warm mist unit include:

  • Higher moisture saturation
  • Works better with medicated products
  • Quieter because it does not have an internal fan
  • Generates heat in cold weather

Cool mist units are now much more common, largely because they eliminate burn hazards, making them safer to use in homes with children and pets. There are also cool mist models that purify the moisturized air. These units are considerably more expensive, but they are worth considering if you want the safety of a cool mist design but are worried about health issues. Additional benefits of cool mist units include:

  • Better energy efficiency than warm mist units
  • Generates cooler air in hot weather
  • Tends to cover more space than a warm mist unit

Humidifier Size and Capacity

While all room humidifiers are portable, there is a considerable range in size. Humidifier size can be identified in several ways, including the size of the water holding tank, the amount of water it will put into a room per day, or the square footage of the space it can effectively humidify.

At the small end are tiny 1/4-liter models small enough to sit in an auto cup holder with a USB plug-in power connection. At the large end are console models that hold up to 6 gallons of water and can put 12 gallons of water into the air daily, covering 3,600 square feet of space. These large models are effectively whole-house humidifiers. Capacity is usually denoted on the packaging, but it should not be confused with moisture output, which will be more than the water tank capacity. Water tank size is often a convenience decision since a large tank requires less frequent filling.

While it's tempting to choose a large-capacity unit, this may be a bad idea. If the humidifier is too large for the room, condensation will appear on the inside of the windows, and bacteria and mildew could grow in this environment. Take measurements to determine the correct room size you are looking for. Models for 700 square feet are more than adequate for a typical bedroom or living room. Very large room humidifiers are usually suitable only for homes with large open-concept layouts with good airflow throughout.

Control Precision

Another variable to consider when choosing a portable room humidifier is the control feature. While some humidifiers offer very basic moisture control with two or three variable fan speeds, others may have a built-in digital hygrometer to indicate the moisture level in the room and a humidistat that you can set for the unit to cycle on/off to maintain a precise level. Unless you want to monitor the room's moisture level and manually adjust settings to maintain it, these automatic measurement features are handy and worth the extra cost.

Humidifiers with digital electronic controls generally offer more convenience and greater precision than those with mechanical analog controls.


How long a humidifier will run between fillings depends on several factors, beginning with the size of the water reservoir. Portable room units are sold in varying sizes of water reservoirs, from one liter to five gallons or larger. A 2-gallon will usually run for 12 or more hours on low, but a 1-liter will require refilling every eight hours or so.

The runtime will decrease substantially if the unit is operated on a high setting or if the air is especially dry. Packaging or product description will usually denote how long the unit will run on a filling.

Ease of Handling and Maintenance

Some water tanks are a little harder to remove and refill, and some lift off easily. Decide whether the weight of a full tank could be a problem for you. Take time to inspect the unit to see how easily the water tank removes from the base.

Also, note if the model will require filter changes. If so, check on the availability of those filters, as well as how easy they are to change. Consider purchasing a couple of filters along with your new humidifier, as maintenance is crucial to reduce the risk of bacteria and unhealthy air.

Evaporative models have wick filters that trap dust and particles. Some units have two-stage filtration, which is important for removing allergens. Mineral deposits in the water form white dust that accumulates on the furniture in the room, but some filters will trap these deposits and reduce the presence of dust in the moisture that is expelled into the room. Those with hard water may benefit from using distilled water in their humidifiers, reducing the build-up of scale and mineral deposits.

All humidifiers require regular cleaning to reduce bacterial growth. Check the product information as some models have dishwasher-safe water reservoirs, which makes cleaning easier. The base of the unit also requires manual cleaning regularly.

Noise Level and Settings

Expect some operating noise from a humidifier, but if the unit is for a bedroom, you may want to look for one with a low/silent setting for night use. So-called "silent" models often are not entirely silent, but that can be an advantage since the faint white noise of a humidifier can be a soothing background noise that drowns out other household sounds.

You should have at least two noise settings on the unit—high and low options. Ultrasonic humidifiers are considered the quietest to operate since there is no boiling of water (hissing) and moisture is expelled in a very fine mist.

Safety and Health Features

Many models have safety features where the unit will shut off automatically when the water reservoir is empty—a must-have feature. If you cannot tell from the packaging, this is certainly worth asking the retailer. Otherwise, you need to be diligent to shut it off when it runs dry.

A humidifier with a built-in hygrometer will shut off automatically when the desired air humidity is reached, preventing over-saturating the air, which can encourage mold. Some cool mist humidifiers have UV light features or special tank coatings that kill bacteria in the water. Some units even glow soothingly as a nightlight.

Humidifiers vs. Diffusers

It's common to confuse a humidifier with a diffuser. They look similar and affect the air in your space. Here are the major differences:

  • A diffuser is a small appliance (and smaller tank) designed to disperse essential oils into the air for aromatherapy. It will add a tiny bit of humidity into the air, too.
  • A humidifier is a larger appliance designed to balance moisture levels in the air.
  • There are also some hybrid humidifiers designed with reservoirs for scented oils that allow the units to provide aromatherapy.

If your goal is to disperse essential oils into the air for their healing properties, a diffuser is your best bet. If your goal is to raise the humidity in a space to capture the health benefits of moister air, choose a humidifier. A hybrid humidifier gives you the best of both worlds.


Warranties on room humidifiers are generally one year for replacement, but there are some models with more robust warranties, offering product replacement for a failure occurring within two or three years of purchase. You will generally pay a little more for a humidifier with a long warranty. In reality, these are rather trouble-free appliances, and it's fairly rare for them to fail within the warranty period.

It's rarely a good idea to invest in an extended warranty for a humidifier at the time of purchase. Portable humidifiers are relatively affordable and eventual replacement usually is more economical than the cost of an extended warranty—most of which will still expire well before the appliance fails. Nor does it usually make sense to repair a humidifier that has failed; purchasing a new one is usually the better long-term strategy.

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  1. Humidifiers: Ease skin, breathing symptoms. Mayo Clinic.