When wildfire smoke affects air quality, air filters can help

In recent years, wildfire smoke has ravaged large swaths of the United States — from Northern California’s devastating 2020 wildfire season, to the orange-brown haze that has drifted from Canada into the eastern half of the country this spring and summer. Major cities such as San Francisco, New York, Chicago and Washington, D.C. have taken turns experiencing some of the worst air quality in the world.

How bad is the wildfire smoke in your city? Use our tool to find out.

There are a number of precautions you can take if your air quality is compromised. In addition to wearing a mask, staying indoors and upgrading your home’s HVAC filters, you can try a portable air purifier, also known as an air cleaner, to reduce hazardous pollutants inside your home.

Here’s what you should look for in an air purifier.

How do air purifiers work?

Air purifiers are designed to clean the air in a single room, using filters or electronic air cleaners to remove particles and gaseous air pollutants or kill microorganisms.

Studies have shown that the fine particles known as PM2.5 — which make up most of the particles in the wildfire smoke — can be reduced by the use of portable air purifiers.

The best purifiers have a HEPA filter and a large fan that can push air through a fine mesh to trap particles, The Washington Post has reported. Models with a carbon filter can absorb odors and reduce the smell of smoke indoors.

The U.S. government has not established any standard to determine how well an air cleaner works, other than that used by the military, the Environmental Protection Agency says. There are also standards set by private trade associations.

“Standards for air cleaners now focus only on particle removal,” the EPA says. No standards assess “the comparative ability of air cleaners to remove gaseous pollutants or radon and its progeny.”

Do I need an air purifier?

If you’re trying to determine your indoor air quality, the best way is to use your senses. “Does it look a little hazy in your house? Does it smell a bit?” says Meredith Bauer, assistant director of the Environmental Protection Agency’s San Francisco office, who manages the wildfire and smoke team.

But if there are lower levels of particulate matter, they might not be so easily detectable without the help of air sensors. And some people are susceptible to lower levels, so check in on how members of your household — including pets — are feeling, she says.

What to consider when shopping for an air purifier

Consumer Reports continuously tests air purifiers for how well they remove particles from the air, says Tanya Christian, home and appliance reporter. The purifiers that top their rankings consistently have a HEPA filter and a large fan. Particularly when dealing with wildfire smoke, carbon filters are helpful because they remove the odor.

When it comes to cost, expect to spend more money if you’re trying to purify a larger space. If you’re just looking to clean a bedroom, for instance, you could pay under $350 for an air purifier that’ll do the trick well. It’s always better to err on the side of getting a larger rather than smaller unit, though, because it can filter out contaminants more quickly. One thing to look out for when shopping is the cost of the filters, which you’ll have to replace regularly.

Regardless of whether you have an air quality issue, Consumer Reports recommends running your air purifier 24/7, even if it’s at a lower speed. During events like the wildfire, run it at a high speed (though, fair warning, this may be slightly noisy depending on your product).

While you can certainly order an air purifier for delivery, that may take a few days. Hardware stores are stocking them on the shelves. Home Depot has “seen increased demand for air purification products in the areas impacted by wildfire smoke, and we’re sending in more inventory where it’s needed,” says spokesperson Beth Marlowe.

What do HEPA and MERV mean?

HEPA stands for “high-efficiency particulate air” and refers to a type of pleated mechanical air filter, according to the EPA. These air filters can theoretically remove more than 99.9 percent of airborne particles with a size of 0.3 microns. “Particles that are larger or smaller are trapped with even higher efficiency,” the EPA says.

MERV stands for “minimum efficiency reporting values,” meaning a filter’s ability to capture particles between 0.3 and 10 microns. You could see a MERV rating from 1 to 16. The higher the value, the better the filter is, according to the EPA.

How to choose the correct size for your space

Look at the air purifier’s clean-air delivery rate, or CADR. The higher this number, the more particles the purifier or cleaner can filter and the larger the area it can serve, the EPA says. Presuming a ceiling height of eight feet, the EPA recommends devices of a minimum CADR of 65 for a 100-square-foot room.

This increases in proportion to the surface size of the room, meaning the EPA advises a minimum CADR of 130 for a 200-square-foot room, a CADR of 195 for a 300-square-foo room and so on.

Caring for your air purifier

It’s important to clean air purifiers periodically and make sure the filters are not clogged. “The most important thing is to keep it dust free. If the air intake and exhaust grills are clogged, it’s not going to be able to do its job,” says Carolyn Forte, executive director of the Good Housekeeping Institute Home Care and Cleaning Lab.

Her advice is to first unplug the unit and check the cleaning instructions in the care manual. (If you don’t have the physical manual, you can find it online.) In most cases, you can give it a good vacuuming, using the soft dusting brush tool. “Start with low suction and then increase if needed,” she says.

Some units have multiple filters that may need to be cleaned or replaced. Some are washable and some are not. If your filters are washable, give them a quick rinse under warm water and let them dry thoroughly before putting them back. Forte cautions that most HEPA filters in air purifiers are not washable, but sometimes you can take out the filter and gently vacuum it. Find replacement filters from the manufacturer, at a big box store or from an online retailer.

Also wipe off the outside of your unit with a slightly damp microfiber cloth. And mind where you place the unit, Forte says, to make sure it has plenty of room for air to circulate around it. “Don’t stick it too close to a corner,” she says.

Making the most of your HVAC system

Even if you can’t get a portable air purifier, there are small things you can do with your central air conditioning system or heat pump to help. “The best thing people can do right now is change your furnace filter,” says Francis Dietz, vice president of public affairs at AHRI, the trade association representing manufacturers of HVAC equipment. Even though your filter should be replaced every few months, just do it today no matter what.

Dietz says to make a trip to your local big box store if you need a filter. And don’t assume that buying one with a higher MERV rating is the best plan; just get the same type of filter you already have. “The higher the MERV rating the tighter it is,” Dietz says. “So the air has to have more pressure to get through it and if your system is not designed for that it can harm your system.”

It’s too late to add an air purifier to your whole-house system to deal with the current situation, but Dietz says if you want to plan for the future talk to your HVAC contractor about options. “For now the system you have now and the filtration will be fine for you. Don’t open your windows. Keep your air conditioning on. If you want an extra measure of protection, if it’s 65 degrees out and the air conditioner won’t run because it’s not that warm in the house, set your thermostat to fan, and keep that going. It will circulate the air through your filter.”

Can you make your own air purifier?

An air cleaner can help remove indoor pollutants and reduce the spread of pathogens such as the coronavirus. (Video: Jayne Orenstein/The Washington Post)

Yes. The EPA’s Bauer says this is a good option. “We’ve actually had our Office of Research and Development test the do-it-yourself filter systems — they work,” she says. As The Washington Post’s Lena Sun demonstrates above, you can fashion an air purifier with four 20-by-20-by-2-inch MERV-13 air filters, a 20-inch box fan, good scissors, duct tape, pen, measuring tape and strings.

First, duct-tape your filters into a cube-like shape, ensuring the “air flow” arrows are pointing inward. Also, make sure the pleats are vertical.

Next, secure a cardboard sheet that matches the size of the bottom of the cube, to serve as a base of the purifier. Attach the cardboard to the bottom of the filters with tape.

After that, put the fan on the opposite facet of the cube (or the top of the cube). Ensure there are no gaps between the fan and the inside of the cube. Put duct tape over any gaps.

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