We started with Energy Star's list of energy-efficient air purifiers because it collects important information in one place: cleaning rates for smoke, dust, and pollen, plus ozone emissions and filter types.
We only considered fan-and-filter air purifiers for our lineup because ion generators produce ozone, which can cause health problems—negating the purpose of an air purifier. We also left out products designed for garages or workshops, and eliminated contenders you can't buy online.
Efficacy was our main concern, so we looked at the nearly 370 air purifiers that remained to find those with the highest Clean Air Delivery Rates (CADR) for smoke, dust, and pollen. We preferred air purifiers that could clean a larger space at least five times per hour—the standard set by the Association of Home Appliance Manufacturers.
Due to the abundance of data available from Energy Star, we didn't conduct any hands-on testing for this review. We supplemented this data with additional research into customer reviews and manufacturer resources.