IQAir HealthPro Plus Hospital Grade Air Purifier

Despite the best efforts of the filters in our air conditioners and furnaces, pollen and dust particles can settle into carpets and upholstery. Mold spores can grow in moist areas. And if there are pets or smoke involved, there can be even more particulates in the air.

Whether you suffer from allergies or just want to eliminate the smell associated with all this particulate matter, a good air purifier can be an essential accessory in any room. But how are they different from the filters we already have in our regular AC?

MORE: Our ultimate guide to the best Prime Day deals this year

All that depends on the purifier. Most models circulate air through a HEPA (High-Efficiency Particulate Air) filter, and often more than one. HEPA filters are certified to trap particulate matter as small as 0.3 microns, which covers dust, pollen and most bacteria. Some purifiers boast a medical-grade Hyper-HEPA filter that will go down to 0.003 microns — enough to pick smoke out of the air.

In conjunction with this, the more high-tech air purifiers can employ an extra line of defense. Some models use an optional UV light that renders many micro-organisms sterile, and an activated charcoal filter that can actually pull in and neutralize toxins through electrostatic attraction. There are also models that can ionize incoming particles, which are then sucked in by metal plates or other treated substances.

For a measure of general effectiveness, you can look for a rating on most air purifiers called the CADR — Clean Air Delivery Rate. It’s a number that represents the cubic feet per minute (CFM) of air that has been cleared of all the particles of a given size. These ratings are recognized by the federal government and can be found on most devices. If you can’t find them, the number is fairly easy to calculate: Just take the CFM on the air purifier and multiply it by the percentage of a certain particle (smoke, pollen, etc.) that the machine can remove.

• One of the first things you’ll want to consider when buying an air purifier is the kind of room you’ll be using it in. When it comes to price, this is usually the primary factor. A workhorse unit that can handle an entire living room and kitchen is going to run you significantly more than a machine that’s meant for a home office for good reason.
• Are you looking for protection from allergies or just need to freshen up the air? A quick look at the specs for the purifier should tell you what particles it can effectively remove from the air. Again, a HEPA filter is going to do the trick for most common irritants and odors, including pet hair and dust. But if you live in a smoker’s house, look into something more robust.
• Much like your air conditioner, you’ll likely be keeping an air purifier on for as long as you plan on breathing the air in that room. In a lot of cases, that might be all day, so power consumption matters. Frugal users might want to check out the wattage specs on prospective models. There are also features that can mitigate that electricity drain, such as timers. In most cases, your air purifier won’t be running all the time. It’ll cycle the air through a few times an hour, and you can adjust that number more or less with most models.
• Another thing to figure into your price point are the filters. Like your AC, there’s upkeep involved. Check not only the price of your filter, but the frequency with which you’ll need to replace it.
• Since they’re meant for indoor use, most air purifiers are better looking than, say, that wall AC unit you had in your dorm room at college. That said, few people want them as the focal point in a room. If you’re getting one for a small room, you likely want a small purifier — or at least one that’s nondescript.