The answer to this question will depend on the type of dehumidifier you have and how often it is used. Generally, filters should be replaced every 3-6 months and coils should be cleaned at least once a year. If your dehumidifier is being used in an area with high levels of dust or mold spores, then filters should be replaced more frequently, and the coils should be cleaned more often. Regular filter replacement and coil cleaning will ensure that your dehumidifier is working properly and efficiently. Additionally, replacing filters regularly can also help to improve indoor air quality as it helps to reduce dust, pollen, pet dander, smoke, and other airborne particles.