How Often Should You Replace an Air Purifier and Dehumidifier Filter? Depending on usage intensity, air quality, and environmental factors, the majority of filters in a combination air purifier and dehumidifier should be changed every three to six months. Nearly every three months may be necessary for homes with pets, smokers, or excessive humidity. Even though they appear clean, HEPA and carbon filters eventually deteriorate and lose their efficacy. Original Source: https://hydrofluxsingapore.website3.me/how-often-should-you-replace-an-air-purifier-and-dehumidifier-filter