Even the best air purifier is only as good as its filter. Over time, filters fill up with particles—dust, dander, mold spores, smoke—and their performance drops. If you don’t replace the filter, your purifier can actually start recirculating contaminants.

Most HEPA filters should be replaced every 6 to 12 months, depending on use and air quality. Carbon filters (for VOCs and odors) may need to be swapped every 3 to 6 months, especially if you’re dealing with chemical sensitivities or strong household smells. Pre-filters often need more frequent cleaning or replacing—monthly or bimonthly in dusty homes or those with pets.

Look for units with filter replacement indicators, but don’t rely on them alone. If you notice a drop in airflow, increase in noise, or a return of odors, those are signs your filter is saturated—even if the light hasn’t turned on. Mark your calendar with replacement reminders or use your phone’s reminder app to stay on top of it.