Humidifiers - Warm vs Cool mist

Your reasons for wanting or needing a humidifier could be many. Your home may suffer from low moisture levels during the dry winter months (especially if you use electric heat).  Your children may have respiratory issues, and the doctor has recommended that you boost the moisture level in their bedroom.  It could simply be for your own personal comfort.

As far as the types of humidifiers go, as far as the "portable" or stand-alone models are concerned, there are generally two options:  Cool Mist or Warm Mist.  Now there are other types, but these are the most popular, and rather than list the hundreds of possible variations, I'm going to talk about the simple humidifiers available at places like Wal-mart and various department stores.

First, a basic understanding of how each type works....  Obviously, each puts moisture into the air, but they use different methods of doing so.

Cool Mist

Cool Mist humidifiers have a water tank which must be filled with water.  If the water tank is allowed to run dry, the humidifier will stay running, but no humidity will be added to the air.  Water passes through the unit (usually a tray at the bottom) to a separate compartment with a "wick" which absorbs the water. This wick is a large mesh-like material which has a lot of surface area, and is extremely absorbent. I have included a picture here, taken from the website.
Humidifier Wick
Above the wick is a fan which pulls air past the wick.  Because of the large surface area of the wick (which is saturated with water), quite a bit of moisture is pulled from the wick into the air, where it is then blown by the fan into the room.  Since this moisture is typically room temperature or slightly cooler, these humidifiers are defined as "cool mist".

Warm Mist

Warm Mist humidifiers come in a few varieties.  Some have a basin, some have a tank.  All are filled with water and use heat (a heating element) to make the water evaporate into the air. If they run out of water, most of the newer ones shut off automatically.  Many have a "medicine cup" where liquid medication designed for humidifiers can be added.  The warm mist passes by this compartment and helps bring it into the air along with the mist.  Warm mist humidifiers used to be dangerous to toddlers, because they would get extremely hot (especially if allowed to run out of water), and they were also dangerous when tipped.  Most are much safer now, and will shut off automatically when tipped or when out of water, preventing the scalding-hot temperatures of their predecessors.

Features to look for

  • Humidistat - usually allows the humidifier to shut off once a certain level of humidity is reached.  This will help keep the room from becoming over-humidified.  Too much humidity (over 65%) is bad, and can help encourage mold, will cause condensation on windows, and can increase bacterial growth.
  • Auto-shutoff - very important for warm mist humidifiers, as they are a hazard if the heating element stays on when the unit runs out of water.
  • Easy-cleaning - All humidifiers must be cleaned on a regular basis (usually weekly).  This helps discourage bacterial growth.
  • Quietness - While warm mist humidifiers are usually fairly quiet, Cool mist humidifiers can be very loud.  Larger, slower fans are better than small, fast ones.  A cool-mist humidifier with various fan speeds is better than a humidifier with only 1 fan speed.
  • Capacity - How often do you want to be refilling your humidifier.  Look for one with large water-capacity.
  • Room Size - As with many appliances, humidifiers are usually underrated.  Go with one with a suggested room size slightly larger than yours.
  • Replacement Wick Cost (cool-mist only) - Don't buy solely on the price of the humidifier itself.  Check to see how much replacement wicks cost, as you will need to replace them throughout the year.  A higher-priced humidifier with cheaper replacement wicks will often cost you less in the end.

Pros and Cons

Warm Mist Cool Mist
  • Cheaper long-term cost, as there aren't wicks that require replacement.
  • Water is often boiled, killing any bacteria. However, since bacterial thrives in a warm environment, the warm moisture may contribute to the development of other bacteria in the room.
  • Better in locations with hard water.
  • May contain a medicine cup - an added feature.
  • Generates heat - good if placed in a cold room, not so good if placed in a room that's already too warm.
  • Higher long-term cost. Wicks must be replaced from time to time.
  • Essential for water to be kept "fresh".  If bacteria is contained in the water, it will be pulled into the air.
  • Worse in locations with hard water. Wick will require replacement much sooner, and it may take longer for air to become humidified.
  • Will not effect the room temperature very much (if at all).
  • Generally considered "safer" for toddlers as they do not have a heating element.

Really, neither type is a whole lot "better" than the other, and only you can choose which type is best in your situation.  If the humidifier is going to be placed in a child's room, and you're still unsure, ask your doctor which he/she recommends and why.  Your doctor can make a recommendation based on safety issues as well as bacterial factors that may come into play.

Disclaimer: All information on this page is to be taken as opinion and not as fact.  I disclaim all liability for anything that happens to anybody as a result of this existence of this page, any other pages on this site, or any other companies, people, places, or pages, that have been mentioned, referred to or linked to.  Use this information at your own risk.