Not all filters are created equal. Peak performance is only realized when genuine Vornado Carbon filters are used. Usually your carbon filter's ability to trap odors and gases decreases over time and airflow becomes obstructed as debris builds up. To assure peak performance, it is imperative to change your filter(s) 4 times per year using only genuine Vornado filters. Peak performance is only realized when genuine Vornado Carbon filters are used. Others may claim to be compatible with Vornado units, but the Vornado Air Purifier is calibrated to achieve a 99.97% capture rate only when used with Vornado Filters.