Contributed by Sandra Brown, MD of Cabarrus Eye Center (Concord, NC).
Humidifiers respond to three laws of physics:
Boiling, evaporation, and cavitation.
Warm mist humidifiers boil water to create steam. These humidifiers went out of fashion for awhile because they tended to harbor bacteria, which liked the temperature and chronic wetness. Many warm mist humidifiers are now equipped with internal UV lights that zap bacteria and most have small fabric filters to soak up the water minerals and keep them off the heating element.
Disadvantages of warm mist humidifiers are:
1) unless you are constantly on top of it (or use only distilled water), despite the filters the heating elements tend to build up crusted mineral debris which is hard to clean off
2) the humidity tends to stay at ground level if you have the humidifier on the floor
3) they will hiss and spit, especially as the mineral build up increases, and
4) lower output compared to other types. Warm mist humidifiers are usually touted as the “most comfortable” source of humidity and also the “cleanest”. I have a small one that I place on the bed right beside me when I have a cold but I don’t use it at other times.
Evaporative humidifiers all contain a fan and a wick. One end of the wick is in contact with the water supply and it simply pulls water up itself, thereby exposing it to the air movement generated by the fan, which dries the wick out by sending the water into the environment. A big evaporative humidifier can really kick it out, some large models are available that will handle 1000 square feet of space for 24 hours.
Advantages of evaporative humidifiers are:
1) greatest output
2) can be placed on the floor and the fan will push the humidity widely.
1) wicks require replacement
2) not a ‘clean’ system unless you are diligent about rinsing the tanks and base with chlorine water
3) noisy fan operation.
My personal favorite is the Vornado double-tank humidifier which has a 3-speed fan and a humidistat to shut down when the humidity rises above a set point (this is analog not digital). The fan is by far the quietest I found when I was on my “replace the humidifier rampage” and there is nothing sophisticated about the tanks (no little pop-up valves) so the unit has a long life-time. Filters are hard to find locally and are pricey, and they do not clean well (forget the vinegar soak) but great deals can be found on-line; it is a lot easier to replace a filter than to scrape a heating element. I have acquaintances who complain about the tanks ‘glugging’ when they drain water into the base, which is true; I find it much less bothersome than a rackety fan. The Vornado fan pitch to me is a nice white noise. This is my baseline humidifier in the wintertime; it handled 1600 square feet of house in arid west Texas if left running on low during the day and medium at night. Also, if you run out of water there are no safety risks as the fan simply dries the wicks fully. You can order on-line at Vornado.com
If you want to shop locally, key features are the fan noise and the ease of filling and replacing the water tank…I hate having to maneuver a heavy tank into just the right spot to engage the pop-up valve, especially on my way to bed.
Ultrasonic humidifiers were the rage about 10-15 years ago as they were the first alternative to the old Vicks boil-it or the clunky, loud evaporative humidifiers. They work by “jiggling” water into a bunch of little droplets (cavitation) which are then blown up and out by the fan. If you watch one in operation, you can see that it has the most obvious “steam draft” appearance of the three types. If you ran one in a bedroom the room would get a “dry ice smoke” effect. Ultrasonic humidifiers bombed because of the “white dust” phenomenon, wherein you got a lovely mineral haze all over every flat surface. Using distilled water mostly solved the problem but was too inconvenient and expensive for most people and the style languished.
However I note that ultrasonic humidifiers are back, in cute shapes like Miss Piggy and Kermit (found at WalMart and Bed Bath Beyond, to name two). I have also seen descriptions in swanky home catalogs describing them as having features that prevent the white dust problem. Ultrasonic humidifiers have some definite attractions, including high output and quiet operation. Of all the humidifiers I have used, ultrasonics also gave me the greatest subjective experience of being in a moister environment – like a shower but cool.
I would say, shop carefully for the white-dust-prevention feature and be sure you believe it and are willing to deal with it (replace a $2 filter every 2 days?). A small one in an office or bedroom might be a nice supplement to a larger evaporative unit that handles the whole house. If anti-germ features are important to you, read the box…this is a cool system but not a sterile one.