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Why get an air purifier? Take your pick: There's smoke from widespread fires, airborne viruses, dander from pets, and the generally poor air quality from car emissions. If you're looking to invest in an air purifier, I'd argue that getting a smart purifier is the better bet.

This new class of air purifiers are wifi-enabled and usually have a corresponding app allowing you to turn the purifier on and off remotely or as a result of triggers through an automation. They also tend to give you more detailed information on what they're pulling out of the air, and best of all, can tell you precisely when to replace the filter. Usually, the rule is every six months, but that depends on how much use your purifier has seen and the conditions it has been under. The price of those filters can add up over time, so knowing more precisely when to replace them means you're getting the most out of your purifier.

I've tested all the air purifiers on this list and like them all a lot—the important thing is to determine which one is best for you. I've outlined a few factors to consider below.

What types of filtration to look for

Most purifiers have a series of filters, including a pre filter (which removes bigger particulates like dust or pet hair), a HEPA filter, and a carbon filter. While we focus a lot on HEPA filters, HEPA won't do anything about VOCs, odors, and gases; that's what you need carbon for.

How powerful of a purifier should you get?

Most purifiers say right on the label how big a room they are meant for, but this is expressed in square feet; since purifiers treat the air in a room, this math should take into account the cubic feet of air in a room, which takes the height of the room into account, too.

According to Mike Feldstein, founder of Jaspr, a smart air purifier company, there's another factor you should take into account. What you really need to know about your air purifier, he says, is how much air it moves and how quickly it does so, because this will allow you to figure out how many exchanges of the air in a room you'll achieve in an hour. For the average home, four to eight exchanges an hour is good, says Feldstein. (For medical settings, you want 10-15 exchanges.)

How fast the air moves is referred to as CADR (clean air delivery rate) and the CADR number indicates how many cubic feet of air are moved per minute. If it's not in the product manual, you can usually search for the product specs online and find that info there.

So, how do you apply that to your room? You'll have to do a little math. Take the CADR from the purifier specifications and multiply it by 60 (60 minutes in an hour). Now divide that by the volume of your room (height x length x width). For instance, if the CADR is 430 and your room is 10'x10'x15', the math is:

(430*60)/(10*10*15), which simplifies to or 25,800/1,500, which is 17.2.

That result is your ACH (air exchange per hour). That means the air in the room is exchanged 17.2 times an hour, well more than is necessary. In this case, the purifier can accommodate a much larger space, or will be fine on a lower setting.

Location counts

Purifiers shouldn't be hidden or tucked against walls. To work their best, they need to be in the center of spaces. This can be frustrating, since purifiers have cords that can be tripped over. For that reason, it may be worth considering purchasing several smaller purifiers that can live on tabletops, instead of bigger floor units in fewer locations.

I review a ton of products in a year, so if they're still here after six months, that's a real compliment. A solid year after receiving it, I use the Dyson Hot+Cool every damn day, but that's mostly because it is also a decidedly good fan that can almost replace an AC, and a great room heater. In fact, the purifier aspect is kind of a side benefit of the Dyson line, but that's no matter, it does a good job of it, but it does not do a great job of it, by its own stats. A dedicated air purifier will deliver better results, and during fire season, I keep a secondary purifier in my living room with the Dyson. In fact, Dyson refuses to release a CADR rating for their purifiers, which is the standard most purifiers use. Still, it's effective in most everyday situations to remove odors and dust, and you can't beat a three-in-one functionality. My only other complaint is that you can do no more than turn the machine on and off from the face of it, otherwise it requires you keep track of an annoyingly small remote control that I'd prefer they emulate within the app.

The Mila is exquisitely designed. It's clear that the device adn app were highly thought out for user experience, and I enjoy having the Mila in my bedroom. It's reliably quiet, even though I opted for the most powerful filter (called "The Overreactor" which doesn't offend my sensibilities at all, really). Perhaps that's my biggest issue with the Mila, that by giving people a number of options for what filter they want, they're forced to decide what kind of pollutants they're concerned with, when really all the filters do roughly the same thing at various strengths. A purifier should simply clean the air of dust, dander, virus, and VOCs, which makes me wonder why you wouldn't always get The Overreactor. Still, I can't deny that the purifier does the job well, and I was impressed at the longevity of the filter I bought.

I was already a fan of AirThings, as I have a few of their air-quality sensors around the house (I live in a place affected by wildfires and air quality warnings). This year they released the Renew, and I've been happy to get my hands on it. While it is refreshing to unwrap a compact and unfussy smart purifier, there is no denying that the Renew is going to stick out in your home—it looks like an old-school computer tower. Still, it cleaned my office faster than any of the other purifiers. Unfortunately the capacity is still pretty small. I really liked the visual interface of the app, and it was fast and easy to get reports of what was happening in the room. I am hopeful AirThings will release additional models. It's worth noting the high price of the Renew, but when you look at the fact that there are four filters instead of the traditional three, it might be worth it if you're looking to really scrub a space.

The Dreo is, for lack of a better term, girthy. The relative proportion of the tower to the size of room it should clean (150-300 sq feet) is out of whack. Still, it's like 20 pounds so I've been too lazy to move it out, and it has resided in a room precisely that size, where it has reliably cooled and cleaned for the last few months. Almost four feet tall, the Dreo is a lot like having a small rocket ship in your home, but one that delivers a refreshing breeze. Dreo fans are, hands down, my top recommendation for indoor cooling. They have a unique "natural" setting that feels like a breeze and I really liked that the Dreo tower delivers that breeze nearer to your face than most tower fans. Even though the Dreo wouldn't be my first pick, it's well-priced and when I did construction in the room including drywalling, I was impressed by how quickly it cleaned the air.

I have air purifiers for a reason: We are still living in a pandemic; I have wildfire smoke each summer so bad the air turns orange; my Doberman sheds like crazy. While it would be nice if the purifier was charming looking or fancy, mostly I just want it to clean the damn air, and I'd rather err on the side of caution, all things considered. Coway has a stellar reputation in the purifier space, and this new smart purifier, the IconS, does a good job—with a few caveats.

The Coway is off-white and looks less industrial than other purifiers. The IconS is also bigger, but could be mistaken for a piece of modern furniture. I didn't like how loud the purifier was when it was on full blast, but most of the time, you'll use the purifier in a lower setting. I thought the CADR was low for the size and price of the purifier, but in the size space it was noted for (about 600 sq ft), it did the job as promised. I kept it adjacent to the kitchen to see how fast it would clear kitchen VOCs, a particularly tough job, and per the app and my own nose, it did so within 30 minutes.

If you take the time to do the math on the space you're trying to purify, and ensure that the filter you purchase is well placed in the room, a smart purifier will do the rest of the work for you. It will even notify you when it's time to change the filters. I've tested all of the air purifiers on this list, and any will be a solid choice; it's just a matter of figuring out which is the best for your home.

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