I was reading the other reviews. This filter perfectly fits humidifier model HM1280. I have been using this humidifier for about four years non stop all day long and all night long. And yes, you do have to change the filters regularly every month or every month and a half. That is how these types of humidifiers work. There is nothing so wrong with this product that is warrants only 2 stars. The only reason why I did not give the product and excellent rating is because I have had to design a timing system to keep the humidity at a constant level throughout the day/night allowing the humidifier to turn itself on when the humidity gets below a certain level.