Smoke outside, safer air inside? What N.C. residents need to know

By Will Atwater

When Canadian wildfire smoke turned North Carolina skies hazy and sent air quality into the unhealthy range last month, a short walk outside — or even just breathing indoor air — became risky for some people with asthma, heart disease and other respiratory issues. 

Wildfire smoke contains fine particulate matter, which can trigger asthma attacks and heart problems in the short term and contribute to chronic disease years later. And no matter how well a home is sealed, that smoke can seep into homes through cracks, vents and mechanical systems, making it hard to avoid — even with the windows closed.

Though the worst of the recent smoke has passed since fires in Ontario have been brought under control, Canadian wildfires continue to burn, particularly in western provinces, and there are several months left in the wildfire season.

In North Carolina, the remnants of Hurricane Helene left hundreds of thousands of acres of storm‑damaged trees and debris strewn across  western parts of the state. Combined with this summer’s drought and extreme heat, that fuel load creates what experts say could be prime conditions to spark giant fires here.

But even when wildfire smoke fills the skies, North Carolinians can take action to mitigate its risks to their health. Some simple changes homeowners can make — even with limited budgets — to their household filtration to create safer air indoors.

Small particles, big problems

“Even though those fires [were] far away from us in North Carolina, that smoke can travel hundreds or even thousands of miles down the coast, so you do not have to be close to a wildfire to be affected by its smoke,” said Andrew Whelan, director of communication strategies for CleanAIRE NC, a group that advocates for better air quality in the state. 

He explained that fine particle pollution that’s part of smoke, such as PM2.5, is one of the most harmful forms of air pollution, simply because of its size. 

“It can penetrate deep into the lungs and enter the bloodstream, where it can cause all kinds of problems from there,” he said. “When you say PM2.5, what the 2.5 means is that these are particles that measure less than two and a half microns in diameter, which is less than the width of a human hair. We’re talking about extremely small particles that you can’t see, you can’t necessarily smell, but you’re breathing them in.”

Because of that, those particles can have powerful effects on the heart and the cardiovascular system. 

Multiple studies have shown that when there’s extra PM2.5 in the air, that emergency department visits for heart and lung problems can spike, and they remain higher for days after the pollution has cleared. 

“Populations that are particularly vulnerable might include children, older adults, people with pre-existing heart disease or heart conditions, pregnant people, and certainly folks who are outdoor workers,” Whelan said. “Even people without those respiratory issues may notice they’re experiencing health trouble during periods of elevated smoke.”

Smoke gets in your house

Wildfire smoke can get into homes even when windows and doors are closed because houses are not perfectly sealed, according to a spokesman for the U.S. Environmental Protection Agency who responded to questions by email. 

“Outdoor air flows into buildings through openings, joints, and cracks in walls, floors, and ceilings, and around windows and doors,” the spokesperson wrote. “Smoke is made of tiny particles and gases that can slip through these small openings.”

Homes with specialized HVAC systems, such as those with a fresh air intake or an Energy Recovery Ventilator, can also pull outdoor air in. However, during a time of wildfire smoke, the spokesperson noted, it is important to shut fresh air intakes and to set systems to recirculate.

Changes in pressure can also influence how much smoke makes its way indoors, they said. 

“When air is being drawn out by exhaust fans and range hoods, it can create a vacuum that pulls outside air back in through openings and leaks.”

To protect indoor air during a wildfire smoke event, the agency recommends several steps to reduce smoke levels indoors. 

The first is to consider creating a clean room to help keep smoke and other particles as low as possible during smoke events. Homeowners can also buy portable air cleaners, making sure to read tips and avoid products that intentionally produce ozone.

Another helpful step is to install a high-efficiency HVAC filter [heating, ventilation and air conditioning], the spokesperson wrote. 

“Choose one with a MERV-13 rating [minimum efficiency reporting value] or as high a rating as your system fan and filter slot can accommodate. If you have an HVAC system with a high-efficiency filter installed, run the system’s fan as often as possible by setting the fan to ‘On’ instead of ‘Auto’ to remove particles while the air quality is poor.”

The agency also recommends avoiding activities that create more indoor air pollution, like smoking, vacuuming, frying or broiling meat, or burning candles or wood.

What to look for

Using high-efficiency HVAC filters, portable air cleaners and do-it-yourself air cleaners can all help reduce indoor PM2.5 during a smoke event, according to the EPA. 

“Portable air cleaners can reduce indoor PM2.5 by about 50-80 percent during wildfire smoke events, and DIY air cleaners can perform similarly to commercial units,” the EPA spokesperson said. 

Portable air cleaners and DIY cleaners are designed to handle one room, while HVAC filters can improve air quality throughout the home, according to the agency. Using portable air cleaners with upgraded HVAC filters can provide even greater protection.

For reducing smoke levels indoors, the EPA suggests selecting a portable air cleaner with a clean air delivery rate for smoke that is at least two-thirds of the room area in square feet. Select an air cleaner that uses mechanical filtration with high efficiency filters (such as a HEPA filter or high efficiency HVAC filter).

Practical steps for homeowners

Single-family homes are not as airtight as people think, particularly older homes, according to Matt Green, an indoor air expert and the president of Brucker, a company that represents HVAC manufacturers and engineering firms. 

He said there are many ways for smoke to infiltrate a home.

“There are multiple paths for infiltration,” Green said. “These paths include penetrations for hose bibs, chimneys, furnace venting, hot water heater venting, poorly sealed window frames, etc.”

So, homeowners have to actively manage the air inside when there’s smoke outside.

“Anytime the pressure inside the house is less than the ambient exterior pressure there will [be] infiltration,” Green said. “Many appliances such as gas clothes driers, bathroom exhaust fans, kitchen hoods, hot water heaters, and furnaces exhaust directly to the outside resulting in the pressure inside the home being less than the ambient exterior pressure. 

The first step to controlling the indoor air quality is to close and seal all windows and doors, turn off exhaust fans in the bathroom, kitchen and especially whole-house fans. 

“Don’t run gas clothes driers,” Green said. “If the home has a fresh-air ventilation system, energy recovery ventilator, or heat recovery ventilator, shut it off or set it to recirculate. Then switch the thermostat fan setting from “Auto” to “On” so the blower runs continuously and air passes through the filter around the clock, not just when there’s a call for heating or cooling.”

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