Any number of purifiers is better than none. But in general, models are built to filter the air in a room of a specific size, whether that’s 200 square feet or 400. The experts at Blueair state, “For optimal results, your air purifier should be placed in the room where you spend the most time, or where the air quality is the worst. If your asthma or your allergies keep you awake at night, running your air purifier in your bedroom sounds like the best choice.” If you need it with you at all times, some compact purifiers are easily portable, making it effortless to move it from room to room.
It's also important to consider where in the room to place the purifier, keeping air flow and circulation in mind. The Blueair experts explain, “Air purifiers have an inlet where the polluted air is drawn in and filtered, and an outlet where clean air is pushed out. Place the air purifier where the air can circulate freely in, out and around the unit, away from walls, furniture and other objects that may stop the air flow.” They also recommend putting your air purifier at least four inches away from any potential obstacles but as close as possible to the pollution source (e.g., windows), while avoiding tucking it into a corner.