Clearing out air pollutants in large rooms is a big job, and you’ll need a purifier that’s built to tackle it, preferably one with multiple speed settings and a combination of filter types. HEPA filters collect the most common indoor contaminants, but look for one that has a “True HEPA” filter, which means it is certified to capture 99.97 percent of particles down to 0.3 microns in size. A big space can benefit from a purifier that comes with an ionizer to assist in taking out pollutants more quickly. It will also help the internal filter last longer. Another useful feature is Wi-Fi connectivity, which allows you to control the purifier with a smartphone or some other mobile device. It also lets you turn the purifier in your home on or off from any location, even if you’re on the other side of the world.