After my wife had 3 years at home all had dry cough, especially when we came out of the holidays, and no doctor could find something we came even to change anything on the indoor climate on the idea. In the heating season, we only had about 35 percent humidity measured in the room. With the humidifier we bring it to 50 percent, and the cough is almost gone. Of course, very excited. Use almost exclusively distilled water (about 3 liters a day). The unit we turn on only when we are in the room. The fan is barely audible in the first stage. The second stage is clearly audible but we imagined it to be worse. To compare with a fan, the whirling air in summer. Can entertain you still super. The replacement filter we get much cheaper at an online pharmacy. We do not want to miss the humidifier. The cough is almost gone and the indoor climate considerably more pleasant. Of course, you have to periodically clean the machine and only use fresh water!