How wood-burning stoves affect indoor air quality

With historically low temperatures hitting large swathes of North America this winter, home heating is a topic of much discussion. It’s hard to beat settling down in front of a crackling fire or the glow from a warm wood stove. In fact, more than 13 million households in the U.S. have some sort of wood-burning heat source.

The old saying "where there’s smoke, there’s fire" certainly goes the other way too … So what’s all this smoke doing to our air quality? And how can we keep warm and still enjoy the crackling heat of the hearth without harming our health? 

Let’s dig into these questions and find out!

Before we get right to it, here's a look at what types of pollution are caused by burning wood. Burning clean, dry wood in your stove or fireplace creates a different kind of smoke than, for instance, a forest fire. With high-quality, properly prepared wood, the main pollutant of concern is particulate matter (of various sizes). Particulate matter (What is PM?) is still the driving pollutant in wildfires, but these massive blazes also contain all kinds of other nasty gasses and chemicals caused by the combustion of materials other than wood. For the full details, check out this post on the 2020 forest fire season.

What does using a wood stove do to the levels of particulate matter in the home? 

In a nutshell: Wood burners increase average levels of indoor particulate matter.

According to a recent study in the United Kingdom, average indoor PM2.5 levels are about three times higher and about four times higher for PM1 during the period in which stoves are lit compared to the period in which they are not lit. 

What does this mean for our health?

The World Health Organisation limit for exposure to PM2.5 over a 24-hour period is mean = 25 µg/m3.  So when the stove is burning, the air inside is not safe to breathe for more than 24 hours. Unfortunately, there have been no safe levels determined for PM1 as of yet. Learn more about healthy air thresholds over at the Plume Labs knowledge base.

In terms of understanding your exposure, the authors of this study recommend thinking about "the increased average exposure seen during stove use in the context of other exposures during your day. For instance, from cooking, sitting in traffic, or going walking on a day where outdoor air pollution levels are high. They all contribute.”

How can you keep your stove running and still breathe free?

When interviewed by The Guardian, Rohit Chakraborty, a co-author of the study, said, “If people want to use [wood stoves], we recommend minimizing the time the stove is open during lighting or refueling.”

Wood burners cause less indoor pollution than open fires. “But every time you open the door, you reduce the stove to an open fire and particulate matter floods into the home.” The peaks take an hour or two to dissipate. “But by the time it comes down, someone opens the door again to refuel and you get spike after spike,” Chakraborty said. Some burners have filters, but these only reduce the pollution being vented outside.

Some people without central heating rely on wood burners for heat, and Chakraborty did not call for a ban. “We should leave it to people to decide, but they should at least know what’s going on, and, of course, don’t use it if you don’t need to.”

If you’re curious about the indoor air quality in your home, and in general, you can sign up for the free Air Quality 101 course offered by Plume Labs.

The more you know, the better you’ll breathe!

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