Cleaning up the woodstove

How to enjoy the fire while reducing harmful smoke

By Alex RoslinAlex Roslin

82_istock_woodstove

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We heat with wood eight months of the year at our home in the rolling Appalachians of Quebec’s Eastern Townships. How could we not love it? The crackle, the dancing flames, the smoky bouquet, the snug ambience—no wonder sparking a fire is the first thing cottagers do on an off-season weekend.

So we followed the news closely when, in April 2009, the City of Montreal banned all new installations of fireplaces and woodstoves. (Wood-pellet stoves are still legal.) In BC, where constricted mountain valleys collect thick clouds of woodsmoke, the Town of Golden prohibits new installations of woodstoves and fireplaces, and replacements for existing devices must be high-efficiency, low-emission models certified by the US Environmental Protection Agency (EPA) or the Canadian Standards Association (CSA). Houston, BC has gone a step further, requiring removal of non-certified units by the end of 2010.

The problem is the toxins that stoves and fireplaces exhaust outside, which then make their way back inside. Wood­smoke contains at least 100 dangerous pollutants, including particulate matter (commonly called soot), carbon monoxide, volatile organic compounds (VOCs), and other toxins, that can lead to headaches, asthma, and lung cancer. Environment Canada says burning wood in a non-EPA-compliant stove for nine hours releases as much particulate matter as a car driven 18,000 km. The question is, how can cottagers enjoy the fire while reducing health hazards?

Ban the baddies

In 1988, the US stopped the sale of “old belchers,” as critics call stoves and fireplaces that don’t meet the EPA standards, but they’re still legal in most of Canada, where public education has been favoured over a ban. Stoves certified by the EPA cut particle emissions by 70 to 90 per cent. They use advanced combustion technology to burn particulate matter and gases to completion, reducing pollutants and creating more heat with less wood. Fortunately, Canadians are slowly coming around. Since 1997, the number of non-certified stoves and fireplaces in use in Canada has dropped by about ​40 per cent, from 3.8 million to 2.3 million, while certified devices have nearly quadrupled to one million.

Keep smoke outside

Don Fugler, a senior researcher at the Canada Mortgage and Housing Corporation and an authority on indoor air quality and woodsmoke, says that a system that’s properly set up should not smoke. “People like that nice woodsy smell,” he says, “but it isn’t a good thing.”

One of the biggest reasons smoke gets out has nothing to do with whether or not you’ve got a certified device. It has to do with the set-up of your stovepipe (the pipe that runs from the stove to the wall or chimney) and your chimney (which conducts smoke up and away from the fire or stovepipe). In our house we use an EPA-certified stove, but we still got a cloud of smoke billowing out the stove door when we started a fire and when we added wood. Even when the stove wasn’t in use, we had problems: a constant eggy smell of creosote wafting in through the stove from the chimney.

For advice I went to Jan Herald, a senior instructor for Wood Energy Technology Transfer (WETT), the non-profit group that certifies installers of woodstoves and fireplaces in most provinces. She diagnosed our problems right away: cold backdrafting and smoke rollout.

If you feel cold air from an unlit stove when you open its door, you’ve got cold backdrafting. One of the most common causes, Herald says, is a chimney that runs up the outside of an exterior wall, beyond a building’s insulation envelope. When, on the other hand, some smoke can’t rise quickly up the chimney and so puffs back into the cottage as you add wood, that’s smoke rollout. Cottages are often plagued by this problem because they tend to be shorter than houses and have shorter chimneys, meaning there is less draft, so less suction pulling smoke up when the stove is in use. Another culprit is faulty installation—such as a stovepipe with poorly fitted seals, several 90° bends, or a long horizontal section.

With obvious installation issues, plus a short, exterior chimney, we were three for three with the airflow problems that can cause smoke rollout and cold backdrafting. Great.

“The chimney is the engine that makes your system work,” says Herald. “Having an interior versus an exterior chimney is the main difference in stove function.” For many years, the norm was to build chimneys on the outside of buildings. Then researchers started to learn about “stack effect.” This is a pressure difference that causes natural upward airflow in a home or cottage: Warm air rises from the bottom floor up to the attic. The stack effect can be strong enough to suck cooler air that’s in an exterior chimney down into the warmer interior of the house. That’s especially true if that exterior chimney exhausts an appliance that’s low in the building.

If you build a cottage from scratch or install a new stove, put the chimney inside, says John Gulland, the Killaloe, Ont.-based founder of woodheat.org. “We are quite aggressive about recommending interior chimneys, to the point of obnoxiousness. Put the damn chimney through the house and save yourself a lot of agony,” he says.

This article was originally published on October 12, 2010


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