Rabbit Air MinusA2 SPA-780A

The Rabbit Air MinusA2 SPA-780A is so slim you can mount it on the wall, and reviews say it runs extremely quietly and efficiently. Sensors detect the level of air pollution, and the Rabbit Air automatically adjusts its filtering speed to match. Like the best-rated air purifiers, the Rabbit Air MinusA2 SPA-780A includes a prefilter, HEPA filter (to capture allergens including pet dander) and carbon filter (to capture odors and chemicals). This model also adds two more filters: a second prefilter and your choice of an additional bacteria, pet dander or chemical filter.

Rabbit Air purifiers also include an ionizer -- a feature you won't find on the best-rated air purifiers, such as the Austin Air HealthMate (*Est. $490) and IQAir HealthPro Plus (*Est. $900). Ionizers are designed to electrically charge airborne pollutants, which can make them fall out of the air and stick to a filter plate, or to furniture, floors, walls and people. But experts say ionizers often create harmful ozone, which can damage lungs and worsen asthma. Rabbit Air says its purifiers don't emit ozone, but we found no independent tests to confirm this.

Rabbit Air says the MinusA2 SPA-780A can filter the air in an 815-square-foot room. The company also offers a smaller model, the Rabbit Air BioGS SPA-421A (*Est. $330), which omits the two additional filters and is designed for a 600-square-foot room. However, reviewer Ed Sherbenou at Air-Purifier-Power.com doubts these machines have the power to change the air very often in rooms that size.