Warm-mist humidifiers, also known as vaporizers, can make a room feel warmer, allowing you to bump your thermostat down a notch or two without feeling cold. Because warm-mist humidifiers boil water before expelling it into the air, they kill the bacteria that can breed in a humidifier's tank, and they don't require the ongoing expense of filters that must be changed. These models are also quieter than fan-driven evaporative humidifiers, but 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. These models are not recommended for people with asthma, because hot or warm mist can irritate breathing passages.
Because of these issues, we recommend opting for an ultrasonic humidifier, and we name top choices and budget alternatives among warm-mist capable appliances in our discussion of the best ultrasonic humidifiers.
Humidifiers that produce warm mist are generally cheaper than those we've reviewed elsewhere in this report 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. It's not been reviewed professionally, but an earlier version came in at the bottom of the pack in one independent analysis. Its moisture output and ease of use were acceptable but not great, and it received very low scores for energy efficiency.
If you are looking for an even less expensive warm-mist humidifier for a small space, consider the Vicks Warm Steam Vaporizer (Est. $15). It gets a mediocre rating from the one professional reviewer that's rated it -- scoring well for output and noise, but average, or worse, in all other categories. This model has few features and is best for a small room, but its 1.5-gallon tank will produce vapor for 18 to 24 hours. We saw the most feedback at Walmart.com, where it draws a 3.8-star score after nearly 340 ratings and user reviews. Most are happy with the bang for the buck, but durability seems to be an issue. A single report of a near-miss with a fire is troubling.
If you have a larger space to humidify, and a much larger budget, the Air--O-Swiss S450 (Est. $260), might deserve some consideration. 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 Air--O-Swiss 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 3.8-star rating at Amazon.com following 70 reviews. We see some complaints that performance was not as good as expected, but noise is, as noted, the most often-cited negative. 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.