Air purifiers: how do they work and who should get one?

For several decades, air quality in the US was trending up by many measures. Data indicated that fine, inhalable airborne particulate matter, known as PM2.5, was declining in 41 states before 2016.

But the increasing frequency and severity of wildfires has undone that progress “about 25%” in the last eight years, says Jienan Li, a research scientist specializing in indoor air quality at Colorado State University.

Outdoor air pollutants can influence indoor air chemistry, making the air we breathe at home or in the office less healthy, notes Li. Indoor air pollution can exacerbate asthma and other respiratory issues, and lead to “ sick building syndrome ”, a condition with symptoms like fatigue, headache and nausea.

As a result, indoor air purifiers are becoming increasingly popular, with the US market anticipated to more than double from $2.8bn in 2022 to $4.78bn by 2030.

If you are considering purchasing an indoor air purifier, here’s what you need to know.

What’s an air purifier and who needs one?

Air purifiers are usually portable, mechanical filters that capture particulate matter such as dust and fine particles in the air.

Jill Heins, a senior director at the American Lung Association, doesn’t use the term “air purifier”. Technically, these devices “clean” the air, rather than purify it, she says. “Just because air goes through a Hepa filter doesn’t mean it’s free of viruses, bacteria, and other germs.” Most at-home devices may be able to capture viral particles but generally don’t kill them unless they also use other technology, such as germicidal UV light.

According to Li, air purifiers are most important for people who are sensitive to particles because they have asthma, allergies to pollen or dust, or cardiovascular issues, as well as children, pregnant people and the elderly. But at an air quality index of 150 or higher , “like when the wildfires from Canada affected New York air, and the sky was not clear, everyone should consider using an air purifier”, Li says.

How does an air purifier work?

The components of an air purifier are fairly simple: a fan draws in air from the room and pulls it through one or more filters. The gold standard is a Hepa filter (high efficiency particulate accumulator). A Hepa filter can remove 99% of particles as small as 0.3 microns, including dust, pollen, pet dander and some bacteria. Some air cleaners may also include carbon filters, which are effective at removing odors, gases and volatile organic compounds (VOCs).

Some devices have add-ons like germicidal UV or ionizers. The latter became popular in the 80s and 90s for keeping dust out of the air but have since fallen out of favor because they create ozone gas.

The effectiveness of an air purifier depends on factors such as the type of filtration used; the size of the unit relative to the room (most devices are labeled with the size of the space they can effectively clean); and its clean air delivery rate (CADR), a measurement that indicates how much air an air-filtration system can filter per minute.

Proper maintenance like regular filter changes will keep your cleaner running effectively. Heins notes that shoppers should check the cost of replacement filters before purchasing a cleaner; sometimes these can be as expensive as the device itself. It’s a good idea to use air cleaners in conjunction with regular cleaning practices and at least 10 minutes of ventilation daily if the outdoor air quality is safe.

Do I need an air purifier if I have an HVAC system?

Air cleaners target finer particles than HVAC (heating, ventilation and air conditioning) systems and can improve the quality of your air. Li says that those living in a house should aim for one air purifier per floor (though you should still check the CADR of the unit to ensure it can handle the size your space), while those in smaller apartments can get away with one – just move it to the room you spend the most time in: say, from the living room during the daytime to the bedroom at night.

When should I use an air purifier?

You can use an air purifier as much as you like.

If you’re trying to be judicious with energy use, keep track of the Air Quality Index daily and use it when the color-coded system creeps into the orange zone – an index of about 100 or higher. Based on US Department of Energy estimates , air purifiers don’t use a lot of energy: about 75 watts, or as much as a phone charger. You could leave one running all day at a cost of about $120 per year.

Some devices have built-in particulate matter sensors, which measure the concentration of particles in the air and start filtration when levels of PM2.5 are high. However, such sensors do not target ozone, Co2 or VOCs.

Unfortunately, there are few easy, cheap and totally reliable ways to test air quality at home, says Heins. “The American Lung Association does not recommend that people need to routinely test their home environment,” for more than carbon monoxide and radon, both of which can be monitored via a long-term detector in your home, says Heins. Some companies do offer continuous indoor air quality monitoring systems that test for a wide range of indoor air pollutants and “give you feedback, usually to a phone app”, she says, though these systems can be expensive and unreliable.

Related: Are at-home gut microbiome testing kits a scam?

How much does a good air purifier cost?

According to Heins, a good air purifier can cost anywhere from $150 to $1,500. You should be able to find an excellent single-room unit for under $300.

A homemade Corsi-Rosenthal box can also effectively and inexpensively clean air. To make one, you’ll need four or five MERV13 particulate air filters, taped together to form a cube, and a box fan to draw air through the filters. A 2022 study found that a five-filter Corsi-Rosenthal box had a CADR rate of 600 to 850 cubic ft per minute.

What else can you do to maintain good air quality in your house?

“Don’t burn things in your home, whether it be cigarettes, vaping, fireplaces, candles or natural gas for your appliances,” says Heins. The air quality in your home generally drops when you’re cooking with gas . If you have a gas range, make sure you use an exhaust fan while cooking, and open a window if the outdoor air quality is safe.

The fragrance chemicals in cleaners and personal care products can also affect the air quality in your home. Make sure you choose products free from harmful chemical compounds to keep your home clean and smelling fresh . Regularly dusting and vacuuming removes dust particles and pet dander, and is especially important during wildfires, when harmful polycyclic aromatic hydrocarbon (PAH) particles can settle on furniture and surfaces indoors .