Mine is a hard room to humidify because it has forced heat, high 10-ft.ceilings, and covers nearly 500 sq. feet. My previous experience with this size humidifier has been poor. The Vornado, though better than some others, is no exception. During a typical New York winter day, leaving the unit on high fan and "continuous" max setting, results in humidity of 30-34%. Extreme cold and dry can make the level go down to 22% while snow and rain brings it to the 40 and 50% range. I like the fact that this unit is so quiet I can leave it on high all night and hear just a soothing hum. (The large humidifiers are so noisy I need to turn the fan speed down so they never reach a high enough level the rest of the day to come up to par.) Left on continuous "high," this unit needs refills every 15-16 hours, NOT 24 as claimed. Since it has NO automatic shut-off, but will continue running on empty, you must check it continually. On the other hand, the small tank makes for easy carrying and refills, especially suitable for older and weaker people.