Ideally, a mix of both works best. Most air purifier manufacturers give a rough timeline for filter checks or replacement – often every 6–12 months for the main filter, depending on the model. That’s a good baseline to put in your calendar. However, actual usage and environment matter a lot.

If your purifier runs many hours a day in a polluted or dusty city, filters will clog faster. Many modern units have indicators that show filter life or airflow status. Trust those signals. If you notice reduced airflow or the purifier sounding different, it’s worth checking the filter even if the official time isn’t up yet.

Visually inspecting pre-filters every month or two is also smart. Pre-filters often catch larger dust and can be cleaned, which extends the life of the main filter behind them.

So, follow the manufacturer’s schedule as a starting point, but stay aware of how heavily you use the machine and what the indicator lights – and the air quality in the room – are telling you.