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Wildfires and Indoor Air Quality: What You Need to Know

Smoke and other impurities can pollute air in your home


spinner image smokey yellow air in new york city due to canadian wildfires
Smoke from Canadian wildfires has engulfed Manhattan and is getting into indoor spaces too.
Getty Images

As smoke from Canadian wildfires envelops outdoor areas, the air you breathe inside your home can suffer too.

But there are plenty of ways to prevent smoke from creeping in and to improve the overall quality of indoor air.

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To keep wildfire smoke outside, the U.S. Environmental Protection Agency suggests taking these steps:

  • Keep doors and windows closed. The American Lung Association says tucking damp towels along the bottom of windows and doors can help keep smoke out.
  • Set your HVAC system to recirculate mode or close the outdoor intake damper.
  • Avoid using an evaporative cooler or a whole house fan that pulls in air from outside.
  • Use a portable air cleaner with a high-efficiency particulate air (HEPA) filter and a filter for your HVAC with a high Minimum Efficiency Reporting Value (MERV) rating, which measures a filter’s ability to absorb larger particles. A filter with as high a MERV value as your HVAC system can handle will result in cleaner air.
  • If you don’t have access to a portable air cleaner, you can create a DIY air cleaner.
spinner image instructions for a diy air cleaner using a twenty by twenty air filter and a twenty b y twenty box fan attach air filter to back of box fan using clamps duct tape or bungee cords check filter for direction of air flow marked on side of filter
U.S. Environmental Protection Agency

Create Your Own DIY Air Cleaner

There are several ways to build your own air cleaner. Designs involve using one or more air filters in coordination with a box fan and typically work best in a small room, like a bedroom. The U.S. Environmental Protection Agency has instructions and links to tutorial videos to help people make their own. If you do create a DIY version, the EPA recommends these safety tips:

  • Use a newer model box fan with safety features.
  • Do not leave the fan unattended while in use and monitor children nearby.
  • Do not use an extension cord and make sure your home smoke detectors are working.
  • Have extra filters on hand to change them out when they become dirty.

This wildfire event should get people thinking about whether their indoor air quality has been compromised, particularly if they are older or have health issues, says Delphine Farmer, a professor of chemistry at Colorado State University in Fort Collins. She recommends using a portable air cleaner in the room you spend the most time in and wearing an N95 style mask if you plan to exercise indoors.

“When the air outside is really bad, it’s usually better inside,” she says. “But when it’s such an extreme pollution event ... the indoor air is going to be heavily influenced by the outside.”

Wildfire and other pollutants are a problem

Smoke from wildfires isn’t the only thing that can affect indoor air quality. Smoking, frying or broiling food, burning candles or incense and using a vacuum cleaner that does not have a HEPA filter can all have a negative impact. Common home pollutants like asbestos, radon, mold and household chemicals can make your indoor air dirty too.

In fact, the U.S. Environmental Protection Agency (EPA) estimates that indoor air might be two to five times more polluted than outdoor air.

In general, strategies such as proper ventilation and low-cost fixes like air purifiers and filters can all help. While green plants may look nice, experts say they don’t have much impact on the air quality in your home.

Here are some ways to clean up your home’s air environment during a wildfire event and all year round.

Improve ventilation

Most people don’t think about indoor air quality unless they experience health symptoms that can include headaches, aggravated allergies, elevated asthma, fatigue, coughing, dry eyes and skin rashes.

​“We know that particles — aerosols or small solids or liquids suspended in the air, like dust, smoke, smog or oil from cooking — have negative health effects ranging from respiratory lung disease to cardiovascular issues,” Farmer says.

An indoor air quality monitor will tell you the level of particles you have in your house — though be skeptical of those that claim to detect everything — but you can also just use your nose, suggests Farmer.

“If there’s a smoke event or you live near a busy road, you can generally smell or see that the air quality isn’t good,” she says.

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Inexpensive fixes can make a big difference, says Jamie Gold, a wellness design consultant in San Diego and author of Wellness by Design. Normally you might start by opening a window (unless your area is experiencing smoke from wildfires) — a strategy recommended by the EPA to improve air circulation.

“It’s ideal to have the best-ventilated space and as much fresh air as you can get,” Gold says.

Make use of properly installed bathroom or kitchen fans too. Without proper venting from the kitchen to the outside, your home can be filled with grease, food odors and smoke, she adds.

“If you’re not using bathroom ventilation, you can have mold and mildew buildup,” Gold says. “Use fans if they’re working well and replace them if they’re not.”

Focus on air filters and purifiers

Use efficient air filters for your home’s HVAC system and change them every six to 12 months to improve indoor air quality. Look for HEPA filters but avoid ones that use UV light, which can generate ozone, a serious air pollutant, cautions Farmer. Ditto for filters with ionizers or hydroxyl radical generators.

“They don’t do anything that the plain HEPA filter doesn’t, plus they have the potential to introduce toxic molecules into your indoor environment,” she explains.

​Portable air purifiers can filter out pollutants in a room and, along with best practices recommended by the U.S. Centers for Disease Control and Prevention, can be part of an overall plan to guard against germs, bacteria and the COVID-19 virus, according to the EPA. Purifiers pull air through a HEPA filter, explains Farmer, and even the most affordable models effectively clear out aerosols.

spinner image Air purifiers have helped Kathy Przywara, who has asthma, improve her home’s air quality.
Air purifiers have helped Kathy Przywara, who has asthma, improve her home’s air quality.
Courtesy of Kathy Przywara

Kathy Przywara, 58, takes medication daily for asthma, and living in Mountain View, California – a wildfire zone – is challenging. She runs her air purifiers frequently.

“When there are active fires and smoke is blown into the valley, I have more asthma symptoms,” says Przywara, vice president of community for the Asthma and Allergy Foundation of America.

“You can also just buy a box fan and duct-tape a filter onto it, which works really well,” adds Farmer.

If you live in an area where the outdoor air is quite contaminated — say, by wildfire smoke — upgrade the filter in your HVAC system, says Farmer. Get a filter with as high a MERV value as your HVAC system will handle.

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Prevent mold and mildew

Lowering the relative humidity in your house is essential to preventing the growth of mold, bacteria and viruses, says Doug Hoffman, 74, executive director of the National Organization of Remediators and Mold Inspectors (NORMI), a nonprofit in Abita Springs, Louisiana. NORMI educates the public and trains professionals to identify and remove toxic mold.

“Typically, mold, bacteria and viruses thrive in environments where the relative humidity is higher than 60 percent or lower than 40 percent, so stay within that range,” says Hoffman, who suggests using ventilation fans, vacuuming regularly and making sure you have fresh air coming into the house.

For an in-depth look at the humidity environment in your home, a professional may do swab or aerosol testing, particulate counts, and relative humidity and temperature measurements to create an indoor air quality (IAQ) profile.

This can be used to personalize a home solution if problems are found, explains Hoffman. For a 1,500- to 1,700-square-foot home or condo, expect to pay $600 to $1,200 for a comprehensive analysis.

To fix mold issues, experts usually sanitize to lower the microbial count. That may involve fogging the space and wiping it down, or using air purification technology. In severe cases, remediation — removing affected materials — might be required.

Get relief from radon

Radon poses another risk to indoor air quality. This naturally occurring radioactive gas is found in most soil types, and can move up through the ground into your home through the foundation. When present in large amounts, it’s the second-leading cause of lung cancer, notes Gold.

“It’s invisible, odorless and present in many homes at the lower level,” she says. “You may have more people in your home right now — college kids back from school or an elderly relative — or you’re using your basement as a work-from-home space.”

Radon detectors are inexpensive and can be purchased online or at your local hardware store. Professional radon services, which are often more accurate, can also evaluate whether there’s radon in your home.

spinner image David and Daniela Naidu used a radon test and found levels in their apartment were high.
David and Daniela Naidu used a radon test and found levels in their apartment were high.
Courtesy of the Naidu Family

In Boulder, Colorado, David Naidu, 57, and his wife, Daniela, 54, took advantage of the city’s free radon test kit, and took readings over several days.

“We discovered the radon level in our apartment was high, so our landlord agreed to hire a radon mitigation company,” says Naidu.

To reduce the level of radon, the company increased the ventilation of gas below Naidu’s concrete floor, blowing it out of the apartment through a hole drilled into the wall. The couple are relieved the issue has been resolved, especially since they are also in a wildfire zone.

Editor's note: This story was originally published on November 10, 2020. It has been updated to reflect new information.

6 Habits That Improve Indoor Air Quality

  1. Clean cooking vents regularly so they work effectively. 
  2. Turn ceiling fans on. 
  3. Use HEPA filters in your HVAC system and change them every 6 to 12 months. 
  4. Wipe down bathroom surfaces after showering. 
  5. Remove shoes and boots at the door to reduce the amount of chemicals and particles brought into the house.
  6. Wipe moisture from windows and sills.

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