Warm mist only humidifiers (also called vaporizers) can make a room feel warmer, allowing you to bump your thermostat down a notch or two without feeling cold. Warm mist ultrasonic humidifiers (which are covered in their own section) warm water to slightly above 100 degrees Fahrenheit. These humidifiers, on the other hand, boil water (heat it to 212 degrees Fahrenheit) before expelling it into the air, killing the bacteria that can breed in a humidifier's tank. Other pluses are that they don't require the ongoing expense of filters that must be changed and that they are quieter than fan-driven evaporative humidifiers, though they can be noisier than ultrasonic models.
There are, however, some serious drawbacks. They tend to have poor energy efficiency, and minerals from the water can build up on the machines heating plate, requiring periodic cleaning. Plus some experts warn against the use of these machines near children, where curious hands can tip over a humidifier filled with hot water, potentially scalding your child. Vaporizers are also not recommended for people with asthma, because hot or warm mist can irritate breathing passages.
Warm mist only humidifiers are generally cheaper than ultrasonic humidifiers that produce both cool and warm mist, but they do not fare nearly as well in reviews. However, we see some user recommendations for the Vicks Warm Mist Humidifier (Est. $30). Many appreciate the humidifier's performance, but some complain that the noise level is higher than with other warm mist models. We also saw durability complaints. Some owners report breakdowns within weeks or even days after purchase. Leakage is another common problem. Still, based on ample feedback (over 3,000 reviews at Amazon.com, for example) user ratings place it near the top of this category.
If you have a larger space to humidify, and a much larger budget, the Boneco S450 (Est. $260), might deserve some consideration. Under its old Air-O-Swiss brand (it's otherwise an identical machine) it finishes in the lower-half among large-room humidifiers in one expert review, with a warning regarding "potential scalding from high water and steam temperatures." It does better at AllergyBuyersClub.com, where it is called an appealing option for those who don't like ultrasonic humidifiers. Of note, this humidifier is not prone to giving off dust residue -- an issue when using ultrasonic humidifiers in areas with hard water. We see a surprising split decision on noise, with AllergyBuyersClub.com noting that the noise level will likely disturb light sleepers, but another expert citing low noise levels as a plus. Owners tend to side with AllergyBuyersClub.com on that issue.
The Boneco S450 is well equipped. There's a humidistat to monitor room humidity, a decalcification mode for easier maintenance, on/off timers, a tank empty indicator, automatic shut-off when the tank runs dry, a removable water tank for easier refills and more.
User reviews are not particularly plentiful, and are about on a par with other humidifiers (of any design). It earns a 3.7-star rating at Amazon.com following 80 reviews. We see some complaints that performance was not as good as expected, and noise issues are noted somewhat regularly. We also see lots of comments that freedom of the dust generated by ultrasonic humidifiers is welcome. Feedback is better at AllergyBuyersClub.com, a 4.6 star rating, but that's only based on just over a dozen reviews.