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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
(Score: 5, Interesting) by VLM on Monday June 09, @10:08PM (7 children)
The authors probably don't know anyone who owns a wood stove and likely don't live more than a half mile from a Starbucks, so can't expect much from people like that.
Catalytic stoves are more expensive but they pay for themselves generally about 200%. Not 1000% not 101%, figure if you pay $500 extra upfront you'll save about $1000, you can't get a bank CD or stock index fund with a return like that LOL.
Figure a chimney clean/inspect is "like $300+" around here and maybe you can get away with two, maybe three years between sweeps.
The cats are designed to burn out and need replacement as a permanent revenue stream for the stove mfgr and they cost "like $500" so there's that. Someone with a stove is already used to paying like 2x for homeowners insurance so its not really all that much money in the grand scheme of things.
Another thing a city slicker wouldn't know about is cat stoves burn like "a third" less fuel as a helpful side effect. Thats very abstract for city slickers who pay a gas bill; but if you chop/split/haul/stack your own wood, as many do, thats 1/3 less labor (and cost, wood not being free).
As a negative cats are generally pretty ugly, if you're dumb enough you can clog them just like car catalysts can be clogged, and if you're barely competent at fire starting on a good day, they can mess up draft until they get going.
Still, overall a pretty good idea.
One negative is anyone who can afford a cat stove gets a cat stove so the main effect of this ruling is people too poor to buy a cat stove will burn charcoal grills in their house and dumb shit like that so the net effect of this "well meaning" and "generally good idea" legislation will be an increase in human suffering, not a decrease. Then again the people in charge, generally hate the people they're in charge of, so they likely see that as a feature.
(Score: 1, Interesting) by Anonymous Coward on Monday June 09, @11:12PM
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.
(Score: 5, Informative) by fliptop on Monday June 09, @11:55PM (1 child)
I burn wood exclusively for heat in the winter, generally between October to April-May. There are times I've cleaned my chimney mid-winter. I definitely clean it every year in September. I had a chimney fire one year I didn't clean it and that was all it took to convince me it needs cleaned at least once per year.
Our Constitution was made only for a moral and religious people. It is wholly inadequate to the government of any other.
(Score: 2) by Reziac on Tuesday June 10, @03:07AM
When I burned cottonwood I never had to clean the stack. When I burned coal (in really cold weather, wood couldn't keep up) more like once a month. Now I have natural gas and can't be bothered. :)
And there is no Alkibiades to come back and save us from ourselves.
(Score: 2) by Thexalon on Tuesday June 10, @01:17AM
Out of curiosity: What would it take to prevent that planned obsolescence? As in, is it really the entire unit, or one part that if available would be something an average homeowner could replace?
(I say this as someone who was able to fix an electric stove that I suspect many would have replaced without too much trouble, and in general am in favor of fixing rather than replacing more things.)
"Think of how stupid the average person is. Then realize half of 'em are stupider than that." - George Carlin
(Score: 3, Interesting) by corey on Tuesday June 10, @12:13PM (2 children)
Your writing style is unique, sort of like an old guy off on a rant and I could only just follow the points you made. But you might be right, the authors are scientists in the city studying something from a theoretical basis, with assumed use cases and so on.
You say cat stoves, do you mean wood-fired heaters/stoves with a catalytic converter? (Sorry I didn't RTFA). Here in Australia, we don't call woodheaters 'stoves'. And I haven't heard of woodheaters with catalytic converters, but that's not to say it doesn't exist. I live rurally, and am literally sitting by our woodheater (not for cooking, has no facility for that) right now as it's winter, night-time here. I was thinking the article authors were talking about danger to occupants inside the house, but it sounds like they are talking about neighbours? Hence the addition of a cat converter to the flue pipe, I could see how that would reduce particulates, just like in a car. But a lot of the time I open my woodheater door, smoke pours out (if the wood isn't dry) and so we have a nice Chinese air filter thing (Winix brand) which removes PM2.5 from the air. They became popular during COVID and the bushfires around here. It works well and noticeably clears the air. We run it most of the time the woodheater is going, which is usually in the evening because during the day we use the reverse cycle (have solar panels). But, thinking of putting in hydronic heating system to avoid both, but only run the fire for the atmosphere.
I do love sitting by the fire with a Scotch in Winter.
(Score: 0) by Anonymous Coward on Tuesday June 10, @04:58PM
> do you mean wood-fired heaters/stoves with a catalytic converter?
Yes, these have been available in USA for many years. My friends in rural Vermont (cold climate, five acres of hardwood trees) have a nice cast iron wood stove with the optional catalyst. I think they bought it about 30 years ago. It's similar to this model, https://www.countrystoveandpatio.com/shop/c/p/Vermont-Castings-Intrepid-II-FlexBurn-Wood-Stove---Transition-Doors-Classic-Black-Catalytic-Not-Included-x72524243.htm [countrystoveandpatio.com]
Visiting them in the winter, their valley is noticeably smoggy from all the wood heating. The catalyst is meant to reduce the pollution (as well as increasing efficiency, less wood consumed for same heat output).
(Score: 1, Informative) by Anonymous Coward on Wednesday June 11, @12:35AM
The only time it's reasonable to expect smoke coming back in to the house is during a tough start when your kindling is not so good, and you've failed to establish a draft. You definitely shouldn't have that problem when re-loading a hot fire. If that's happening, you need to figure out what's blocking your draft. Hopefully it's not a stack full of creosote.