When it comes to choosing the best humidifier overall, expert reviewers typically place ultrasonic models at the top of their lists. These best of these machines are capable of producing warm or cool mist. They are also quieter than other types of humidifiers and lack a messy-to-clean filter. Their downside is a higher propensity to emit dust -- an especially annoying problem for those with hard water. Remedies include using distilled water or a demineralization cartridge, if one is offered.
In the ultrasonic category, we found the best feedback for the SPT SU-4010 (Est. $80). It earns excellent ratings across the board in one independent test and is named a Best Buy. It's also the Editors' Choice selection at BabyGearLab.com, where Ellen Baker reports that the SU-4010 was "a strong performer in all of our rating areas with an ability to effectively and quietly humidify both large and small rooms via a nice combination of features and overall design." It's also the top rated ultrasonic humidifier at TheSweetHome.com. Though John Holecek thinks that evaporative humidifiers (covered in our discussion of best cool mist humidifiers) are a better value, especially for humidifying smaller rooms, the SU-4010 is his pick for spaces of 400 square feet or larger (up to 500 square feet, as rated by the maker). He notes that it performs similarly to models costing twice as much, such as our previous top pick, the Air-O-Swiss AOS 7135.
This SPT (formerly Sunpentown) humidifier is designed to produce cool and warm mist, with variable humidity levels. This model does not include a humidistat to automatically turn the humidifier on and off depending on the humidity levels in the room, but that's not a deal killer in any of the expert reviews we saw. Holecek adds that the humidistats tested in some other highly regarded models, such as the AOS 7135, proved to be inaccurate, "so that's a wash anyway."
The SPT's pluses include a demineralization cartridge (called the Ion Exchange Filter), which should be replaced every six months to prevent the release of minerals into the air -- a frequent complaint with humidifiers. Other features include overheat protection and a split rotating nozzle to direct mist in two directions simultaneously. This model is energy efficient (using up to 43 watts on the cool-mist setting and 90 watts for warm mist) and very quiet.
While ratings are high for the SU-4010 among experts, there are some disagreements. At TheSweetHome.com, it's held back a little by "those daily tasks that hold back several humidifiers—cleaning and refilling," but others have fewer qualms. At BabyGearLab.com, it's rated at above average in terms of cleaning ease. Pluses include a water tank opening that's wide enough so that you can fit your hand in sufficiently to wipe down most surfaces. For harder to reach spots, "We were happy to find that É this humidifier comes with a small brush to clean the ultrasonic vibrating plate as well as some of the other small spaces in the base, and that the brush fits neatly into the base for storage," Baker says. It also earns high ratings at Baker's site for Ease of Use, even of refilling -- including kudos for a water tank with a "sturdy built-in handle." It also earns a top grade or convenience from an independent reviewer
User reviews are mixed, something that's unfortunately commonplace when it comes to humidifiers. At Amazon.com, more owners are happy than not, but we saw reports of humidifiers breaking down anywhere from a week to four months after purchase, and we also read several reports of leakage, often severe. However, some owners identify the source of the leak as being improperly seating a sealing ring after filling and that carefully following the maker's refilling instructions should eliminate the problem. User ratings, albeit based on less feedback, are better elsewhere, including a 4.1-star rating at Walmart.com following more than 130 reviews.
If you have a larger room to humidify, the Air-O-Swiss AOS 7135 (Est. $180) ultrasonic humidifier continues to deserve consideration. This humidifier can produce warm or cool mist and is suitable for rooms up to about 650 square feet. The water tank on the Air-O-Swiss AOS 7135 is detachable and transparent, which makes it easy to clean and allows you to keep an eye on the water level. A digital humidistat allows you to adjust the humidity in the room to your desired level, though, as noted above, testing by TheSweetHome.com found accuracy to be wanting. This humidifier comes with an Air-O-Swiss AOS 7531 demineralization cartridge (Est. $16), which needs to be replaced every two to three months (or more often with hard water) to prevent the release of minerals into the air -- a frequent complaint with humidifiers. There's also an Air-O-Swiss AOS A200 Hydro Cel (Est. $30), which should be replaced every two months or so to prevent bacteria from taking root in the water tank between cleanings.
While TheSweetHome.com has dropped its recommendation, the Air-O-Swiss AOS 7135 continues to do well in other professional reviews. It's a recommended pick by one independent expert, and its second highest rated humidifier for large rooms. It tests out worse than the SU-4010, the top rated choice there, when it comes to convenience -- rating only good in that regard and with a note that user feedback indicates that the unit is hard to fill and clean (again, both common humidifier complaints). Like the SU-4010, the Air-O-Swiss is aces in all other regards. The expert review at AllergyBuyersClub.com notes that more of the site's staff members own the AOS 7135 than any other humidifier it sells. "All in all, the Air O Swiss 7135 is a sensible and reliable solution for anyone looking to improve the air quality in their home or office," they say.
User reviews, however, are a bit of a mixed bag. Amazon.com hosts the most of these, and owners are of a decidedly split mind. Many are mostly to completely pleased, however this humidifier's overall score is dragged down to 3.6 stars overall by owners that complain about leaking, inconsistent humidity, or mineral dust; the latter is especially a problem for those with very hard water or who skip using the demineralization cartridge. At AllergyBuyersClub.com, feedback is a bit better -- a 4.3 star rating based on more than 50 reviews, with 79 percent of buyers saying that they would recommend the AOS 7135 to a friend.