Can I Use an Air Purifier to Clear My Home of Wildfire Smoke?

Can I Use an Air Purifier to Clear My Home of Wildfire Smoke?

With more significant fires becoming the new normal nationwide, even those people not directly threatened are concerned about what to do about wildfire smoke. Two bits of good news: First, the EPA says (PDF) that “the long-term risks from short-term smoke exposures are quite low.” And second, there are simple, effective ways of getting rid of the wildfire smoke in your home.

As we point out in our air-purifier collaboration with The New York Times (our parent company), keeping your home’s air clean in fire season requires a multipronged approach. Picking up a dedicated air purifier or getting new filters for your central air conditioner are the most effective things you can do. But you can take cheap, simple, and immediate steps using stuff you probably already own, too, such as a mop and a washing machine. Here’s what we recommend.

Invest in an air purifier

A view looking down at the Blue Air Pure 211+ shown next to the Coway Mighty, showing the depth and footprint of the two models.
The Coway AP-1512HH Mighty (right) takes up a lot less visual space than our large-space pick, the Blueair Blue Pure 211+ (left). Photo: Sarah Kobos

First, consider a true-HEPA air purifier. We have an extensive guide to air purifiers, but the basic facts are these: According to the EPA (PDF), wildfire smoke predominantly consists of fine particles in the 0.4 to 0.7 micron range. And true-HEPA air filters are exceptionally good at removing particles of that size from the air. Our top picks, the Coway AP-1512HH and nearly identical Coway Airmega 200M, are well-priced, superb performers, and reliable. They’re powerful enough for rooms up to 350 square feet, which includes most bedrooms and living rooms. The Blueair Blue Pure 211+, our pick for larger spaces, can rapidly clear the air in bigger rooms and open-floorplan homes.

We recommend running either of them on high for an hour the first time you turn the machine on. That’ll clear the air quickly by passing the entire volume of air in the room through the filter four to six times. Thereafter, keeping the machine on low or automatic will keep the air clear, and you won’t be bothered by the noise of the fan: On lower settings, they’re virtually silent.

Physics lesson time: To be rated true-HEPA, an air filter must remove 99.97 percent of all airborne particles of exactly 0.3 micron diameter in a single pass. That size became the test standard because it’s the most difficult for HEPA-type filters to capture. These filters consist of dense mats of fine fiberglass fibers. As the purifier draws air through them, larger particles (1 micron and above) slam into the fibers and stick there, carried by their own momentum. By contrast, smaller particles (below 0.3 micron) don’t “ride the wind” but instead bounce around slowly and randomly, buffeted by the arbitrary motions of air molecules. That slow, wandering path eventually brings them into contact with the filter fibers, where, like the bigger particles, they stick. But particles of 0.3 micron (and by extension, similarly sized smoke particles in the 0.4 to 0.7 micron range) are just the right size to ride the wind but too small and lightweight for their own momentum to drive them into the filter fibers. Instead they tend to slip around the fibers. True-HEPA filters have enough fibers, sufficiently densely packed, to overcome this tendency and capture virtually all these difficult particles—again, 99.97 percent of them—the first time they move through.

Upgrade your HVAC Filters

If you have central air and heating, you may consider a different and cheaper option: upgrading to one of the furnace and air-conditioning filters we recommend. Medium-MERV filters, according to the EPA, “are likely to be nearly as effective as true HEPA filters” at controlling most airborne indoor particles.

MERV stands for minimum efficiency reporting value, and is a measure of how well a central-air filter removes particulates from the air. Medium-MERV filters provide much more filtration than the basic MERV 1–4 filters that come standard with central-air systems, which capture only pollutants visible to the naked eye, such as pet hair and dust bunnies, but not fine particulates like smoke. If you’re not sure which type you have, the most basic filters are cheap and typically green or blue in color, and they look like a loose, flat net of thin string that you can see through easily.

The medium-MERV filters we recommend, rated MERV 8 to 13, are typically an opaque white, felt-like in texture, and pleated like an accordion. In our guide to furnace and air-conditioning filters, our recommendation is a MERV 12 filter from Nordic Pure. A six-pack typically costs about $40. If they’re not available, we also have MERV 12–equivalent recommendations from Honeywell and Filtrete.

A stack of the furnace filters we tested
The filters we recommend, rated MERV 8 to 13, are typically an opaque white, felt-like in texture, and pleated like an accordion. Less effective, basic MERV 1-4 filters are typically green or blue in color, and they look like a loose, flat net of thin string. Photo: Michael Hession

One caveat: These medium-MERV filters can put strain on your air handler. For modern central-air systems, it’s not likely to be a critical strain, especially not in the short term—that is, until the wildfires go out. (Read our detailed reporting on the matter in our main filters guide.) But smoky conditions will clog the filters in as little as half the recommended replacement cycle (usually three months), so we suggest simply replacing the filters once the fires are over. Wildfires or not, if your system is more than 15 or 20 years old, it may not be up to the extra effort of medium-MERV filtration. In that case we recommend buying a portable air purifier, as described above; they aren't cheap, but they are cheaper than replacing your air handler.

Keep your place clean

Regardless of whether you go with the above recommendations, you have other simple, essentially free steps to take to reduce the problem of smoke in your home.

It may seem obvious, but close your windows. Most of the time, outside air contains fewer particulates than indoor air, so open windows are a good idea. But in wildfire conditions, that isn't the case. Closing your windows will help keep smoke from entering your home in the first place.

Even fine smoke particles eventually drop out of the air and settle on surfaces, including floors. We recommend damp-mopping your floors to pick them up rather than vacuuming, which can simply blow them back up into the air. Our picks for dust mop and wet mop do a great job (I use both) and are inexpensive, durable, ergonomic, and washable. But any mop you own will work. For the record, damp-mopping (with the mop lightly wetted, as opposed to wet-mopping, with the mop saturated) won’t damage wood floors.

Smoke particles also settle on your clothes, skin, and and bed. If you’ve spent time outdoors in the smoke, change into clean clothes when you get home. Wash your sheets more often than normal, too. Take a quick shower before you go to bed. And after the smoke clears and the fires subside, clean everything, change all your filters, and breathe easier.


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