How to pick the right air purifier for your home as wildfire smoke descends

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As wildfires ravage Canada, smoke has drifted south into the United States and blanketed skies with a orange-brown haze. The unusual scenes prompted officials to issue Code Maroon warning – the highest for air pollutant hazards – in many parts of the northeastern United States early Thursday.

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.

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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, remove 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.”

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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.

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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.

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Can you make your own air purifier?

Yes, 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.