Particle filters such as HEPA are unfortunately by nature only effective for roughly 6 months, then they are clogged. You can vacuum them to get rid of the bigg

Particle filters such as HEPA are unfortunately by nature only effective for roughly 6 months, then they are clogged. You can vacuum them to get rid of the biggest particles and then use them for another 6 months (total 1 year), but then they are clogged at molecule level and are perhaps only 25% effective of its original efficiency and won't do you any good. The washable ones are not good and the ionization air purifiers without filtration are a scam. Particle filters are the best way to give you good air quality. And unfortunately you get what you pay for. When it comes to carbon filters they don't work for more than 6 months - no matter how good air quality you have. Carbon will absorb till it finds equilibrium then start to release smells and some gases. Shelf life of an opened package is about 6 months even if you don't push air through. Depending on the air quality in your local area (Bombay smog/wild fires/countryside clear skies), your filters will be clogged eventually and a rough estimation is 4-6 months in high polluted areas, and 1 year in less polluted areas). Turn the air purifier off when you have the windows open. It makes no sense to use it if you let pollutants in from outside, even if your indoor quality is bad.