Glossary
HEPA filter
A high-efficiency air filter that captures fine particles such as pet dander, useful in small closed apartments.
A HEPA filter is rated to capture at least 99.97 percent of particles at a very small size, which includes pet dander, dust, and some pollen, rather than just larger visible fur. In a house, dander can spread out and settle across many rooms, but in a small apartment with limited airflow, dander tends to concentrate in the same rooms the pet uses most, which is where an air purifier with this kind of filter is most noticeable.
The filter itself is a physical mesh, not a chemical or spray, so it works by pulling room air through the unit rather than by treating the air with anything added to it. That means performance depends heavily on running the unit near where the pet spends time and on replacing the filter on the schedule the manufacturer lists, since a clogged filter moves less air even if it still looks intact.
When comparing purifiers, check the room size rating against the actual apartment room, since an undersized unit will run constantly on high and still underperform. A common mistake is placing the purifier in a corner behind furniture, which restricts airflow into the intake and reduces how much air it can actually clean per hour.