1. Water Tank Capacity

The larger, the better. If you live in a region with cold winters and sub-zero temperatures or if you reside in a very dry climate with humidity levels below 30%, the daily water consumption of a humidifier can reach 10-30 liters for an average family. This is especially true if your home has a full-fledged supply ventilation system. If you plan to integrate the humidifier into a Smart Home system, manually refilling the tank with such high-water usage will be quite inconvenient. For a sample calculation and a detailed explanation of the physical aspects of air humidity and its impact on health, see the article “Why Relative Humidity is So Important for Health.”

2. Maintenance Effort and Operating Costs

Regardless of the operating principle, all humidifiers require regular maintenance and replacement of consumables. Choose what suits you best, but keep in mind that regular upkeep is unavoidable. At the very least, make sure that all necessary consumables are easily accessible:

• Steam humidifiers (hot steam) require regular descaling, frequent filter changes, and slightly higher electricity costs.
• Air washers, or humidifiers based on the cold evaporation principle, where air is passed through wet filters or a chamber with a large free water surface. These devices demand extra attention to the cleanliness of the chambers and filters. True to their name, air washers not only humidify but also purify the air of dust. However, the collected dust accumulates in the water reservoir, requiring regular cleaning and disinfection. Neglecting sanitation can lead to mold or algae growth, with all the associated consequences.
• Ultrasonic humidifiers, which create a cloud of fine water droplets using ultrasound, are nearly ideal. They are simple, safe, highly efficient, and energy-efficient. However, there’s a catch that many have stumbled upon: ultrasonic humidifiers require distilled water to function properly. Otherwise, your home will quickly be covered in a dense white residue that is difficult to clean. Where do you think the dissolved salts from those tiny droplets go? The water evaporates, leaving behind salts, including those responsible for limescale in kettles, which then settle on your furniture.

So, if your area doesn’t have convenient and affordable access to distilled water, this might not be the solution for you. Alternatively, you’ll need to produce distilled or at least very soft water yourself, which requires time and additional expenses.

3. Humidity Feedback

Most manufacturers include this feature by default, but not all. So, when purchasing, ensure that your device can automatically stop operating once the threshold humidity level is reached — essentially, it should know when to say, “pot, stop boiling.”