Product review (5 stars): Genuine Original Manufacturer's Brand at the Best Price
I have used this filter for many years now. The very best home humidification system by far in my opinion. Some people change these several times per winter, but I have always been successful in putting one in when my humidity first falls below 50% (around the first couple of weeks of November), and leave it in until air conditioning season starts here in central NC (around April). One filter per year.

And calling it a filter is not really accurate. It is simply a foam "sponge" that automatically rotates in a pan of water, allowing the circulating air in my HVAC system to evaporate the water from the foam surface, and increasing the humidity in my home to the level we set on the thermostat/humidistat.