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posted by hubie on Monday June 09, @09:45PM   Printer-friendly

New technologies help wood-burning stoves burn more efficiently, produce less smoke

Oregon State University researchers are gaining a more detailed understanding of emissions from wood-burning stoves and developing technologies that allow stoves to operate much more cleanly and safely, potentially limiting particulate matter pollution by 95%.

The work has key implications for human health as wood-burning stoves are a leading source of PM2.5 emissions in the United States. PM2.5 refers to fine particulate matter with a diameter of 2.5 micrometers or smaller that can be inhaled deeply into the lungs and even enter the bloodstream. Exposure to PM2.5 is a known cause of cardiovascular disease and is linked to the onset and worsening of respiratory illness.

Even though a relatively small number of households use wood stoves, they are the U.S.'s third-largest source of particulate matter pollution, after wildfire smoke and agricultural dust, said Nordica MacCarty of the OSU College of Engineering.

Residential wood combustion, especially the use of inefficient stoves, is also a significant source of other harmful emissions including polycyclic aromatic hydrocarbons, carbon monoxide, nitrogen oxides, methane, benzene and formaldehyde.

"Wood is an affordable, local, renewable, low-carbon fuel that should be an important part of the U.S. energy mix, but it must be burned cleanly to effectively protect health," MacCarty said.

"Folks typically think of pollution as coming from vehicles and industry, but household wood stoves are a larger source—just a few smoky stoves can create a harmful effect on air quality in an entire community."

MacCarty published a paper in the Journal of the Air & Waste Management Association showing that 70% of the pollution emitted from wood stove flues happens at two points in time: when a stove is first lit, and when it's reloaded. MacCarty's team gained that knowledge by developing a new monitoring technique and deploying equipment at a collection of wood stove users' homes in rural Oregon.

According to the Environmental Protection Agency, there are an estimated 6.5 million inefficient stoves in the U.S., most of them models that predate EPA clean-burning standards. In all, there are roughly 10 million wood-burning stoves in the country, or one for every 35 people.

"A lot of the older stoves are essentially just metal boxes with chimneys and they don't incorporate modern engineering principles to optimize heat transfer and combustion," said MacCarty, the Richard & Gretchen Evans Professor of Humanitarian Engineering and an associate professor of mechanical engineering.

"They have no catalysts or secondary combustion to reduce emissions and lower the risk of creosote buildup that can cause chimney fires."

MacCarty's group is developing automated technologies that inject jets of primary and secondary air into the fire to provide just the right amount of air and mixing at the right time and place in the fire. Prototypes are showing about a 95% reduction in particulate matter emissions compared to older models, she said.

The EPA has been reducing the allowable PM2.5 emissions rate regularly since the 1980s. In 2015 it was 4 grams per hour for cordwood stoves, and five years later it was reduced to 2.5 grams per hour. Regulation is driving innovation as stove makers improve their designs to meet certification requirements, MacCarty said.

But wood stoves perform differently in the lab than they do in real life, she noted, and stoves are certified based on laboratory tests—and often designed to pass the tests, rather than to operate well in someone's home.

"It's difficult to measure wood stove emissions in the field, so there has been relatively little in-use performance data available in the past to guide designs," MacCarty said. "Our study introduces a new system that makes collecting real-world emissions data more practical."

The project included Oregon State undergraduate student Jonah Wald and was a collaboration between OSU and the nonprofit Aprovecho Research Center based in Cottage Grove, Oregon. It builds on OSU and Aprovecho's ongoing work on efficient combustion for cooking with wood in the developing world.

Roughly 2.7 billion people rely on open fires for cooking, MacCarty said, and her team has been designing efficient cook stoves for them to use instead.

More information: Samuel Bentson et al, In-situ measurements of emissions and fuel loading of non-catalytic cordwood stoves in rural Oregon, Journal of the Air & Waste Management Association (2025). DOI: 10.1080/10962247.2025.2483217


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  • (Score: 1, Interesting) by Anonymous Coward on Monday June 09, @11:12PM

    by Anonymous Coward on Monday June 09, @11:12PM (#1406523)

    I once asked our local fireplace/stove guy how often stacks and/or stoves need to be replaced. That was a riot. I forget the exact number, but it was quite ridiculous. I'm pretty sure my stove and stack are 2X or 3X past the service life he suggested. There's an obvious incentive for the stove guy to say you need a new stove, and yeah the catalysts are a racket. This is cheap heat we're talking about, and I have ZERO GUILT about running EPA phase-1 with a baffle plate but no cat. In the Summer, we get wild fire smoke. In the Winter, I look out my window and see agricultural debris burns and/or controlled forest management burns that throw out orders of magnitude more smoke than the worst stove start I could possibly muster. My wood stove is a drop in the bucket.

    They might do better if they simply educated users and/or made hot kindling easier to come by. Not everybody knows how to do a proper start. Some people have no qualms about trying to do a start with damp oak, and others will damp down to the point of throwing smoke continuously and *that* definitely invites the aforementioned creosote build-up.

    Anyway, you pretty much nailed it. The only thing worse than cat stoves is pellet stoves. We had a freak snow storm one year--no electricity for a week because trees here aren't used to snow load. I had heat all that time, and you can't get that with pellet stoves because they rely on electricity. Yes, I could have a generator--but that's getting us away from cheap and it's also getting us away from safe. I got rid of all the propane appliances here. My wood pile might burn if wild fire hits us, but it won't blow up or blow out and make a blow torch near the house. In a true fire storm, your odds are low but every little thing you can do helps.

    You're right about chimney sweep costs too. They seem to have gotten way out of line even for a single story stack like mine. I think my neighbor had to pay $250 for a sweep on a similar stack. I'm lucky I can still do it myself. I'll get perhaps a gallon of soft black soot out at the end of the season. I've never seed the dreaded plastic-looking stuff that's hard to get out and can turn your stack in to a rocket. I must be doing fairly decent burns.

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