Here’s what to look for in an air purifier for wildfire smoke

With smoke from wildfires in Canada blanketing cities in the northeastern U.S., health officials are urging people to stay indoors, and wear high quality N95 masks outside.

But indoor air can be even more polluted than outside air, particularly when smoke particles become trapped in small, confined spaces, as is happening in some homes.

A good air purifier with a high efficiency particulate air (HEPA) filter can help clear the air inside a home or office.

This type of filter can remove at least 99.97% of pollutants, including dust, pollen, mold, bacteria and any airborne particles with a diameter of 0.3 microns, according to the U.S. Environmental Protection Agency. 

“It’s about filtration and ventilation, so HEPA is ideal,” Dr. Leonardo Trasande, a professor of population health at NYU Grossman School of Medicine, told CBS MoneyWatch.

An air purifier with a HEPA filter can cost $1,000 or more if it’s designed for a large space. Consumer Reports’ top-rated air purifiers also start at around $300.

But cheaper, do-it-yourself solutions can also work well, Dr. Trasande said. 

He recommended the “Corsi–Rosenthal Box,” a widely used air purifier design that is easy to build yourself for less than $100. To make it, you need a box fan and five minimum efficiency reporting value (MERV)13 air filters to capture smoke. (The higher the MERV value, the more filtration it provides.) Duct-tape the filters into in a cube and mount the fan on top to capture and filter air.

“It is a good example of balancing cost with optimizing the filtration [times] ventilation calculus,” he told CBS MoneyWatch. 

At the very least, he recommends using air conditioners, which function by recirculating indoor air — thereby reducing pollutants. 

What to look for in an air purifier

Experts say the two most important features of an air purifier are their filter quality and fan size.

“You want to make sure it has a HEPA-certified filter because that means it will be effective on these really small particles that can penetrate your lungs,” Johns Hopkins Bloomberg School of Public Health environmental professor Ana María Rule told CBS MoneyWatch. “They do a really good job of bringing clean air in and removing dirty air from the indoors.”

For maximum effectiveness, try to match the air purifier to the size of the space you plan on using it.

“If it’s for a bedroom, a small air purifier might be enough,” Rule said. “But you might need something bigger for a large home with tall ceilings and multiple rooms.”

“Either contain yourself to a smaller room, or get a bigger, more powerful air purifier,” she advised. 

Air purifier packaging typically indicates the volume of the room it is intended for. 

How much do they cost? 

There are thousands of different air purifiers on the market that range in price from a few hundred dollars to well into the thousands of dollars, depending on how big it is. A sleek design can also drive up the price. 

“Sometimes the price is higher because of its size; other times it’s for the design,” Rule said.

Other bells and whistles beyond a good filter and fan aren’t necessary. “All you need is a good HEPA Filter that is sized for the volume of your space,” Rule said.

Consumer Reports’ top-rated air purifying products have HEPA filters that capture 99.97% of air particles as well as large, powerful fans that help draw in air particles for filtration, explained CR’s home appliance expert, Tanya Christian. 

Most of Consumer Reports’ top-rated air purifiers retail for less than $1,000. Products appropriate for smaller apartments shouldn’t cost more than $300-$400, Christian said. 

Consumer Reports’ top pick?

The Coway Airmega ProX, for $999. A smaller and cheaper alternative is the Blueair Blue Pure 211i Max, which is great for a space up to 635 square feet and is available for less than $300.

Most purifiers use filters that need to be replaced periodically, so consider how much replacement filters cost and factor that into the maintenance cost. Noise levels matter, too, particularly if the unit will be placed in a bedroom and could keep the user awake.

It’s never a bad idea to have an air purifier in the home, especially if it includes smokers or anyone with a respiratory illness like asthma. 

“People with pets in the house use them if a spouse is allergic so they can breathe purified air at night, or cigarette smokers will use them. People certainly bought them for Covid-19, too,” Doug Laher, COO of the American Association for Respiratory Care told CBS MoneyWatch. “It’s always a good practice, because you never know what might be floating around your home, or dust could accumulate over time.”