Meet the teams: Backed by the EPA and DOE, top cookstove designers tackle the heatstove

This post is the sixth in a series introducing the 12 teams participating in the 2018 Wood Stove Design Challenge in November.

By John Ackerly, Ken Adler, and Shoshana Rybeck, Alliance for Green Heat

Cook stoves and international development 

Dean Still (left) with participants at an
Ethos conference near Seattle.

Dean Still leads the team at the Advanced Studies in Appropriate Technology Lab (ASAT) and has been involved with the international cook stove community for decades. He and his team have achieved many key breakthroughs in testing, stove design, instrumentation, and like most researchers and developers, they have had their share of dead ends, disappointments and flops.  

The New Yorker magazine featured Dean in a 2009 article about engineers who need to design stoves that cost no more than $10 so even the world’s poorest people can afford them. So, when we told Dean that cheap stoves by our standards were between $500 and $1,000, he laughed and said, “you would think that should be easy.”

ASAT won a $300,000 grant from the EPA to build a heat stove that makes electricity, thirty times more than the $10,000 that each team is getting from DOE through the Alliance for Green Heat. ASAT has another advantage that only a few teams have in the competition: they operate a testing lab so they can measure changes in emissions and efficiency with each iteration of the prototype.

ASAT's sister group, Aprovecho hosts
annual "stove camps" where innovators
work together to built and test designs

The challenge for ASAT is whether they translate their experience and skill making cookstoves into a successful heating stove that performs well in the lab and in the field. There is a tight timeline and ASAT is new to the way the EPA measures PM and efficiency for heat stoves—and the way that tests will be conducted at the Stove Challenge. Translating lab test protocols to real world emissions may be even tougher for cook stoves and oversight of cook stove labs is weak compared to EPA-approved heat stove labs. But the cook stove community is far more transparent, and test results and technologies are more freely shared in the common battle of a global enemy—daily exposure to wood smoke from traditional cooking practices.

ASAT’s strategy

Dean Still with Prince Charles, who
has been an advocate for the modern,
cleaner cookstoves

ASAT’s stove is unique from the start—it’s a rocket stove.  Rocket stoves are most common as a developing world cook stove where you feed small diameter fuel into an insulated chamber and let it burn the ends of the sticks. Rocket stoves designed for heating are usually called “rocket mass stoves” but the prototype coming to the competition in November 2018 will be a new, high tech, low mass hybrid of the Rocket stove.  

ASAT is using an expansive strategy and are integrating many innovative technologies, from fabric filters to laser smoke sensors that automatically adjust secondary air.  By keeping an open mind, the ASAT team is winnowing down technologies, but the danger is that they are doing this on a very short time-line and the prototype is still going through major changes with less than 6 months prior to the competition.

ASAT's lab in Cottage Grove, OR

ASAT is working to make a stove mostly for the Asian market that can benefit those who struggle to get heat and electricity independently with ultra-low emission rates. The stove will include an electrostatic filter for PM to capture escaping emissions. Dean says his stove will have “jets of pre-heated secondary air that create a zone of mixing like in the carburetor of a car where a combination of high temperatures, residence time and complete mixing result in close to complete combustion. The fan speed, the amount of smoke, CO, CO2, and temperature in stove will be shown on a LTD screen. A PM sensor in the chimney automatically adjusts the velocity of the secondary air jets.”

Thermoelectric technology 

With help from the EPA, ASAT is developing a stove that can be used to cook food, heat the home and create electricity mainly for rural households in Asia that have intermittent or no electricity. To do this, electronic designer and manufacturer Karl Walter and lab manager Sam Bentson have created a new type of TEG that fits into the evolving design. The team is currently working on the fifth iteration and are focusing on how to create reliable electricity in the most inexpensive way possible. 

Sam Bentson, ASAT Lab Manager

The team has been building their own TEG that is making electricity without the use of a water cooling system. Instead, their TEG uses a large radiator that is essentially an aluminum fin designed to move the most air at the lowest wattage possible. With the team solely using a radiator and not including a water cooled system, or even a fan, the model is far less expensive, which appeals to ASAT's dedication to making this as affordable as they can. The team hopes to develop a TEG for less than $100 that creates at least 15 watts of power, using a switch mode voltage regulator and usb connection. Karl Walter says, “Water cooling is great but there is also something to be valued in a simpler, robust approach.”

Creating an affordable cook stove with an attached TEG that does not have “moving parts” is no easy task. Thankfully, with the financial support of the DOE and EPA, ASAT has been able to fully delve into this project and work through the challenges they have faced. Karl says that for their team the largest challenges had to do with temperature differentials and power outputs. He says that finding a “realistic power output was difficult” as well as figuring out “what happens when you overheat the stove.” But, the team is on a two year contract for their EPA project and with a year remaining, they are optimistic about the future development of their product and plan to have a model prototype ready for market testing within the next 4 months.

ASAT follows the old adage to think globally and act locally. Their efforts to create stoves that benefit people around the world have had tremendous support from national and regional organizations and they hope to expose the powerful technology they’ve been working on to a larger audience at the challenge in November. 

Contact the team at:

Dean Still
managerstovetec@gmail.com

Sam Bentson
managerstovetec@gmail.com

Karl Walter
karl@waltech.com

Opinions of top wood stove industry insiders revealed in 1998 interviews

The late Paul Tiegs, one of the
greatest authorities on wood
stoves, conducted the
interviews for the EPA. 

Long before the regulatory debate about wood stoves heated up in the 2010s, the EPA commissioned a series of fascinating interviews with the top wood stove experts in the country on a host of technical and policy issues.  These interviews give a glimpse of the opinions and philosophies of industry and academic leaders at a time when they apparently felt free to go on the record about what became controversial topics. 

The content of these interviews remains very relevant today for anyone interested in a behind-the-scenes look at many of the underlying issues in the 2015 EPA stove and boiler regulations.  The interviewers – Jim Houck and Paul Teigs (who are top experts themselves) – asked questions ranging from whether masonry, pellet, boiler and furnace appliances should be regulated, to the vulnerabilities of catalytic stoves, to how lab testing can better reflect real world use of stoves. 

These interviews remain a valuable resource because each of the nine experts was asked the exact same questions.  Thus, if you are interested in masonry heaters, or catalytic or pellet stoves, or how labs coax the best numbers from stoves, it is relatively easy to scroll down and see how each person answered the question.  Of the nine interviewees, four are from industry (John Crouch, Bob Ferguson, Dan Henry and Michael Van Buren), two from test labs (Rick Curkeet and Ben Myren), two from academia (Skip Hayden and Dennis Jaasma) and one from EPA (Robert C. McCrillis). Their full titles and affiliations are at the end of this blog along with the full list of questions asked.  The full set of questions and answers are in Appendix B on page 58 and can be downloaded here (pdf).

In general, Bob Ferguson and Dan Henry tended to oppose further regulation, and felt, for example, that pellet stoves and wood-fired central heating appliances did not need to be regulated.  Ben Myren tended to favor a blanket approach of closing loopholes and regulating all appliances.  This difference in views between two industry experts and one test lab expert can be viewed through their respective economic interests and how it would affect their livelihoods.  But these interviews also show deeper philosophical differences and illuminate the reasons for their positions, whether they concern the health impacts of wood smoke, consumer protection, profitability, practicality of test method changes, etc.

We have chosen to reproduce the answers to two questions and invite readers to refer to the full set of interviews to find issues that they may be more interested in, such as the impact of wood species on emissions, stress testing to see how durable stoves are, and options to promote or require education or maintenance of stoves by consumers. 

When the Alliance for Green Heat began ten years after these interviews in 2009, much of the content had already been seemingly lost or obscured.  Very few people, for example, knew of the origin or impact of the 35:1 air-to-fuel ratio loophole that allowed pellet stove manufacturers to make low efficiency stoves in order to avoid regulation.  Right up until 2014, state and federal government agencies, along with top industry outlets, continued to propagate myths about pellet stoves.  Even the EPA never advised consumers that uncertified pellet stoves were likely to have lower efficiencies due to the 35:1 loophole they created.  These interviews provide the best information anywhere on how this came to be and what impact it had on the pellet stove industry and consumers.

We chose the question about whether central heaters should be regulated because this turned into one of the biggest issues in the 2015 regulations.  Only one interviewee – John Crouch – saw a causal relationship between the rise of outdoor wood boilers and the 1988 emissions regulations. 

Question: The 35:1 air-to-fuel ratio cut-off for certification has produced two classes of pellet stoves — those that are certified and those that are not. The latter class may have models that are less efficient and have higher emissions than the former. Should the regulations be amended to close the loop-hole and discourage the practice of intentionally designing models with a higher air-to-fuel ratio to avoid certification?

John Crouch, HPBA's
foremost wood stove expert.

John Crouch, HPBA: I wouldn’t use the term “close the loop-hole”. I would say, “is the proper place to cut off the definition of a wood heater?” We all know the whole discussion during the Reg-Neg ignored this emerging category of pellet stoves. So this gets back into my other broader comment, which is, instead of going back in and changing the NSPS in a piecemeal fashion, there needs to be a true revision of the whole thing that deals with the category of pellets and masonry heaters and outdoor furnaces.

Rick Curkeet, Intertek: Yes. The way to amend the regulation is to simply remove the 35:1 air/fuel ratio exemption. This has never been required by fireplaces (they meet the 5 kg/hr minimum burn rate exemption criterion anyway). Pellet units are readily able to meet emissions requirements and the exemption only encourages making these units less efficient to avoid the regulation.

Bob Ferguson, Consultant: The 35:1 cutoff was intended for fireplaces. However, pellet stoves are the only product that even take advantage of the air-fuel exemptions. Fireplaces generally use the burn rate exemption. Pellet stoves probably don’t need to be regulated at all. They are all quite clean burning. Let the marketplace decide if exempt stoves are acceptable. If pellet stove users demand products that use fewer pellets (more efficient), the manufacturers will respond. 

Skip Hayden, Researcher: Yes. In Canada, we recommend that people buy only EPA-approved pellet stoves. We have developed a high ash pellet stove that's operating around 85% and its emissions are about 0.3 g/hr or less. 

Dan Henry, a founder of Quadrafire
stoves is one of industry's most
articulate spokesmen.

Dan Henry, Aladdin: There is no data that indicates that even a poorly operating stove is a dirty burning appliance. They are inherently clean, becoming more and more reliable, and don’t fix them if they aren’t broken.

Dennis Jaasma, University of VA: Pellet stoves are inherently clean burning unless there is something very bad about their design. I am not concerned about regulating the currently uncertified units unless their field emissions are bad compared to certified stoves.

Robert C. McCrillis, EPA: Yes, all pellet stoves should be affected facilities and not subjected to that 35:1.

Ben Myren one of Amreica's most
thoughtful and experienced stove tester.

Ben Myren, Myren Labs:  I agree, no more loop-holes. The new technology stoves that are coming on the market are going to be totally new critters. I don’t think that turning down the air- to-fuel ratio, to make it whatever it is, should get you out of the loop. Some of those suckers have got to be just filthy. I mean you look at the flame. I’ve seen them burn at the trade show; you know, the glass is sooting up on the edges. You can just see it.

Michael van Buren was a technical
expert with The Hearth Products
Association, now HPBA

Michael Van Buren, HPBA: I don’t know what that loop-hole does, whether it really affects the operation of the stove and the efficiency of the stove.

Question: According to a Department of Energy survey out of the 20.4 million households that used a wood burning appliance in 1993, less than 0.3 million used a wood burning furnace as their primary source of heat. Are there enough wood-fired central heating furnaces in use to merit their closer evaluation? How many commercially available models are there? Are there emissions data for them? Should they be certified?

John Crouch: The [1988] EPA New Source Performance Standards killed the indoor furnace industry and created this little loop-hole which the outdoor furnace industry is beginning to exploit and kind of underscores the need for a more comprehensive wood burning regulation which sets out over a several year period to codify all forms of wood burning technology.

Rick Curkeet tested stoves for Intertek
labs and is one of industry's top experts.

Rick Curkeet: I don’t know how many new units are being produced but I’m sure it’s a very small number. Still, one really poor unit can be a significant problem if it’s in your neighborhood. There have never been any standards for testing this type of product for emissions and efficiency. However, we have adapted existing methods and can say that the performance range is very wide. Poor designs may be 30% or less efficient and produce nearly 100 grams/hr emissions rates. Good designs are able to approach certified wood stove performance levels.

Bob Ferguson: I don’t feel there are enough units being sold to merit any activity what-so-ever. There are only a handful of manufacturers. I don’t think there has been anything published--so if testing has been conducted, it is probably a good assumption that the numbers aren’t that good. They shouldn’t be certified, as you would have to develop test methods and standards. The country would be better off using the money to pay manufacturers to phase out of production, sort of like the agricultural method of paying farmers not to grow certain crops.

The late Skip Hayden also worked
at the US Federal Enercan Lab,
back when the federal government
focused more on wood heating.

Skip Hayden: The number of central wood furnaces in Canada, certainly in comparison to the United States, would be higher. In our Eastern provinces, it’s a relatively common add-on to existing oil furnaces. Generally, they are as dirty as can be.

Dan Henry: I think a lot of these are used in rural areas and considering the fuels that are out there, I don’t think they should be regulated. Maybe just a spot check of some sort. I think the only thing that would benefit would be the testing laboratories. If it emits particulate into an air shed where it can have an adverse effect on the industry (my ability to make a living), then yes.

Dennis Jaasma
also ran a combustion
 research lab at
Virginia Polytechnic
 Institute.

Dennis Jaasma: Yes, central heaters merit further evaluation. I don't know how many models are available. I think EPA has done some work on them, but I do not know any results. Yes, they should be certified. They are in danger of becoming extinct if they don't wind up with a certification program.

Robert C. McCrillis: In some localities I think these furnaces are a problem; I don’t know how many are commercially available. I think I can name off six or eight companies and each one makes several models, but I don’t know what the total market is, maybe 10,000 - 15,000 a year. The little bit of testing that we did here, says that they are probably on a par with a conventional wood stove. The way those things work, they have a thermostatically operated draft and when the thermostat shuts off the draft closes, so you get this real smoldering burning situation. Secondary combustion technology probably wouldn’t work. Possibly a catalytic technology would, but I just don’t think it stays hot enough in there. I guess that really depends on the impact.

Ben Myren: I don’t think they should be exempt for any reason. As to the rest of it--are there emissions data for them? I suspect there are. Should they be certified? Yes they should be certified. Nobody should be exempt from the process.

Michael van Buren: I think there should be some type of testing on them.

List of Experts Interviewed

Mr. John Crouch, Director of Local Government Relations, Hearth Products Association (CA) [now HPBA]

Mr. Rick Curkeet, P.E., Manager, Intertek Testing Services (IL)

Mr. Bob Ferguson, President, Ferguson, Andors and Company (VT)

Dr. Skip Hayden, Director, Combustion and Carbonization Research Laboratory (Ontario, Canada)

Mr. Daniel Henry, Vice President, Aladdin Steel Products, Inc. (WA) [now Quadrafire]

Dr. Dennis Jaasma, Associate Professor, Department of Mechanical Engineering, Virginia Polytechnic Institute and State University (VA)

Mr. Robert C. McCrillis, P.E., Mechanical Engineer, Air Pollution Prevention and Control, Division, U.S. EPA (VA)

Mr. Ben Myren, President, Myren Consulting (WA)

Mr. Michael Van Buren, Technical Director, Hearth Products Association (VA) [now HPBA]

Interview Questions

RWC Technology Review

Environmental Protection Agency Order no. 7C-R285-NASX

prepared by

OMNI Environmental Services, Inc.

Beaverton Oregon 97005

1. State-of-the-art of wood stove combustion and emission control technologies.

1. 1.1  Are in-home emission reductions as compared to conventional stoves shown in Table 1 for catalytic and non-catalytic certified stoves reasonable?
2. 1.2  Are efficiencies shown in Table 2 for catalytic and non-catalytic certified stoves reasonable?
3. 1.3  Can catalytic technology for use in wood stoves be fundamentally improved?
4. 1.4  Is the use of manufactured fuel (densified and wax logs) a credible emission

reduction strategy? See Tables 1 & 2 .

5. 1.5  For non-catalytic stoves the heat retention adjustment with refractory material of various densities can reduce particulate emissions. How big an effect can this have?
6. 1.6  Approximately one half of the particulate emissions occur during the kindling phase for non-catalytic wood stoves and more than half for catalytic wood stoves. Are there improvements in technology that can mitigate this problem? Can specially designed high BTU wax logs be used to achieve a fast start and reduce kindling phase emissions?
7. 1.7  Should masonry heaters with tight fitting doors and draft control be classified as a wood stove and be subject to some type of certification even though most weigh more than 800 kg?
8. 1.8  Are the emissions and efficiencies for masonry heaters, based on in-home tests, shown in Tables 1 and 2 reasonable?

9. 1.9  The OMNI staff feels the emissions per unit of heat delivered (e.g., lb/MBTU or g/MJ) is a more appropriate way to rank the performance of wood burning appliances than emission factors (lb/ton or g/kg) or emission rates (g/hr). — Comments?
10. 1.10  Default efficiency values are used for wood stoves. This coupled with the fact that emission factors or rates (not g/MJ) are used to rank wood stoves does not provide an incentive for manufacturers to increase the efficiency of their stoves. — Comments? Should an efficiency test method as described (FR v. 55, n 161, p. 33925, Aug. 20,1990) be required to be used and the results listed?
11. 1.11  Have certified stove design and performance improved since the first certified stoves? If so, how?

2. State-of-the-art of fireplace emission control technology.
1. 2.1  Are the emission factors and efficiencies for the in-home use of fireplaces and inserts shown in Tables 3 and 4 reasonable?
2. 2.2  There appear to be only a few practical design or technology options for fireplaces that will potentially mitigate particulate emissions. — What designs and technologies are available? What retrofit options are there?
3. 2.3  The use of wax fire logs reduces emissions over the use of cordwood. Can the formulation of wax logs be changed to produce even less emissions?
4. 2.4  What are the distinctions between a masonry fireplace and a masonry heater?
5. 2.5  As with wood stoves, the OMNI staff believe that the mass of emissions per unit of heat delivered is a better way to rank the performance of fireplaces than emission factors or emission rates.
3. State-of-the-art of wood-fired central heating furnace emission control technology.

3.1 According to a Department of Energy survey out of the 20.4 million households that used a wood burning appliance in 1993, less than 0.3 million used a wood burning furnace as their primary source of heat. Are there enough wood-fired central heating furnaces in use to merit their closer evaluation? How many commercially available models are there? Are there emissions data for them? Should they be certified?

4. State-of-the-art of pellet-fired wood stove technology.

1. 4.1  Are the emissions and efficiencies for the in-home use of pellet stoves shown in Tables 1 and 2 reasonable?
2. 4.2  The 35:1 air-to-fuel ratio cut-off for certification has produced two classes of pellet stoves — those that are certified and those that are not. The latter class may have models that are less efficient and have higher emissions than the former. Should the regulations be amended to close the loop-hole and discourage the practice of intentionally designing models with a higher air-to-fuel ratio to avoid certification?
3. 4.3  Have pellet stove design and performance improved since the first models were introduced? If so, how?

1. Ramifications of ISO.

5.1 The International Organization for Standardization (ISO) has a technical committee for developing emissions, efficiency and safety test standards for wood-fired residential heaters and fireplaces. (See Table 5 for comparison of the draft ISO method 13336 with EPA methods 28, 5G and 5H.) Do you feel that the EPA methods should be replaced with or be made comparable to an international standard?

2. Correspondence between in-home and laboratory emission test results.
1. 6.1  How accurately do certification tests predict in-home performance?
2. 6.2  How would you design research testing in the laboratory to simulate in-home use?
3. EPA Method 28 strengths and weaknesses.
1. 7.1  Method 28 is in part an “art”. Fuel loading density, fuel moisture, fuel characteristics (old vs new growth, grain spacing, wood density) and coal bed conditioning can be adjusted within the specification range of the method to influence results. In your experience what things have the most effect on particulate emissions? How much influence can they have?
2. 7.2  Burn rate weighting is based on very limited data and the cities from where the data were obtained are not very representative of wood use nationwide (see Table 6). How can the weighting scheme be improved to be more representative of the nation as a whole?
3. 7.3  The equation for the calculation of the air-to-fuel ratio as in Method 28A is in error. The error produces a small but significant difference in the calculated air-to-fuel ratio. Should the method be corrected or should it be left as a “predictor” of the air-to-fuel ratio?

7.4 The assumed mole fraction of hydrocarbons (YHC) is defined as a constant in the air-to-fuel ratio calculations in Method 28A. The mole fraction of hydrocarbons in the vapor phase will vary significantly with fuel and combustion conditions. Should hydrocarbon vapors (more appropriately, organic compound vapors) be measured as part of the method?

4. EPA Methods 5G and 5H correlations.

8.1 The comparison data to demonstrate the correlation between 5G and 5H are limited. Should the correlation between the two methods be reevaluated?

5. Performance deterioration of EPA-certified wood stoves in the field.
1. 9.1  It is the opinion of many in the wood stove industry that catalysts last only five years and that a stove designed for a catalyst operated without a functioning catalyst can produce as much emissions as a conventional stove. — Comments?
2. 9.2  Field studies in Glens Falls, NY, Medford, OR, Klamath Falls, OR and Crested Butte, CO showed that emissions from some catalytic stoves became appreciably worse even after two to three years of use. Inspection of stoves in Glens Falls showed that catalyst deterioration and leaky bypass systems were responsible. Have improvements been made in the design of catalytic stoves to minimize these problems? Is it reasonable to require homeowner training on the proper use of catalytic stoves and/or to incorporate into their costs an inspection and catalyst replacement program?
6. Stress test pros and cons.
1. 10.1  A short-term laboratory woodstove durability testing protocol was developed to predict the long-term durability of stoves under conditions characteristic of in- home use (see EPA-600/R-94-193). It was concluded in that study that damage occurs during those occasional times when a woodstove is operated in the home at exceptionally high temperatures. The laboratory stress test was designed to operate a woodstove at very high temperatures over a one to two week period to predict long-term durability under in-home use. Is this a reasonable approach?
2. 10.2  Should a stress test be made part of the certification process?
7. Feasibility of developing separate emission factors for dry and wet wood and for

softwood and hardwood species classes.

1. 11.1  Optimum wood moisture for low particulate emissions seems to be in the 18% to 20% range. Are you aware of any data that will allow the impact of wood moisture to be isolated from other variables? Could it be different for wood from different tree species?
2. 11.2  Wood from different tree species clearly burns differently. The chemical make-up and density of wood from different tree species is different. For example wood from coniferous trees has more resin than wood from deciduous trees. It is believed that particulate emission factors will be different for wood from different tree species. If this is true different parts of the country may have different emissions factors for residential wood combustion. Are you aware of any data that document different emission factors for wood from different tree species?

8. Routine maintenance.

12.1 Would routine maintenance of stoves once they were in a home reduce particulate emissions? Would this be more relevant for catalytic stoves than non-catalytic stoves? Would this be relevant for pellet stoves with electronic and moving parts?

2. 12.2  Should the home owner be provided with a maintenance manual or a training course at the time of purchase? Should a maintenance program be part of the purchase price particularly for catalytic stoves?
3. 12.3  What would the key elements of routine maintenance be?

- end -

Sample Wood Smoke Nuisance Regulations

This outdoor wood boilers in Morgan
County Utah was somehow found not
to be a nuisance by a County Judge. 

Updated: May 2022 - Many jurisdictions in the Western US have “burn bans” that disallow the use of wood or pellet stoves when air quality is very poor, often in conjunction with weather inversions.  Nuisance regulations, on the other hand, apply when one person is creating excessive smoke that bothers an immediate neighbor.  That person may be using an EPA certified stove, an old stove or an outdoor or indoor boiler.

In the US, wood smoke complaints are handled locally, and more often than not, local officials are at a loss to handle complaints effectively. There is also a range of standards by which excessive smoke is measured.  Lack of resolution between neighbors is all too common, due sometimes to a lack of a clear nuisance standard for that town or county, or simply due to a lack of the ability or willingness to enforce a nuisance standard.  

The Alliance for Green Heat and many in the wood heating community support strong nuisance regulations and urge local officials to train their staff to enforce them.  Often, the problem is less about the stove technology and more about poor operator behavior. Many stove owners do not understand that their energy solution should not be their neighbor's problem.  Reducing fossil fuel use is a great benefit of wood stoves, but when a single stove is too polluting, or there are simply too many stoves in a valley or town, solutions are needed.  Pellet stoves are often an excellent solution from a pollution standpoint.

In areas with frequent inversions and in urban areas, limiting the new installations of cordwood stoves is often a good solution.  And, not allowing the installation of uncertified, second hand stoves is also a good solution.  Requiring permits and professional installation can also help.  

Sometimes, standards are less important than the discretion and findings of a local health official.  In Massachusetts, for example, a City Commissioner of Public Health has wide discretion to order someone to stop burning wood, as a Commission did in June 2017 after local residents complained of smoke from a restaurant. The 6-page decision found that a $65,000 scrubber performed poorly and ordered the owner to stop burning wood and charcoal.

If a jurisdiction has no written standard or regulation and does not allow the kind of discretion a health commission in Massachusetts has, the sample provisions below offer an excellent starting point for the jurisdiction to adopt.  Most jurisdictions use "opacity" as a measure of smoke - meaning the ability to see through it.  An opacity of 20% or lower is often listed as acceptable, but not always.  In some regulations, a specific amount of start-up time is exempted, ranging from 6 to 20 minutes in these sample regulations. However, many wood stove experts say 20 - 30 minutes is often the time needed to get a fire without visible smoke.

The Ringellman chart or scale was developed in 1888 and is still sometimes used and referenced today.

The Ringellman scale was adapted by the US Bureau of Mines.

The Alliance for Green Heat has noticed an increase in complaints about wood smoke.  We know that in many cases excessive wood smoke results from burning unseasoned wood, caused in part by the shortage of seasoned firewood this year.  Too many people with wood stoves wait until the fall to order wood and too many firewood distributors try to pass off unseasoned wood as seasoned.

The proposed ban of stoves in Utah has also brought the issue of “responsible burning” to the forefront, with industry calling for EPA certified equipment to be exempt from any ban.  These nuisance provisions, with a few exceptions, make no distinction between the kind of device that is being used, and focus solely on how well the operator is using it. 

STATES

We have updated the links to current laws as much as possible, but check the actual language in the current law, not on our summary to be sure of how the law or regulation works.

Colorado

No person shall cause or allow the emission of smoke exceeding twenty-percent opacity from any flue or chimney, except for a single fifteen-minute period for cold start-up. Any emission in excess hereof is hereby declared to be a nuisance and is prohibited.

Maine (2013)

A person who operates in a densely populated area an outdoor wood-burning device that produces visible emissions, measured as any opacity, totaling 12 minutes in any hour that cross onto land or buildings immediately adjacent to a dwelling or commercial building not owned by the owner of the outdoor wood-burning device creates a nuisance.

Massachusetts (2022)

Massachusetts Department of Environmental Protection (MassDEP) regulations limit visible smoke (or "opacity") and prohibit air pollution that places people at risk, interferes with property uses, threatens natural resources, or creates nuisances, such as excessive odor and soot.

Oregon (2014)

Wood smoke in Oregon

* Existing sources outside special control areas. No person may emit any air contaminant for a period or periods aggregating more than three minutes in any one hour which is equal to or greater than 40% opacity.
* New sources in all areas and existing sources within special control areas: No person may emit any air contaminants for a period or periods aggregating more than three minutes in any one hour which is equal to or greater than 20% opacity.

Utah (2021)

* A nuisance is anything which is injurious to health, indecent, offensive to the senses, or an obstruction to the free use of property, so as to interfere with the comfortable enjoyment of life or property. A nuisance may be the subject of an action.
* A nuisance under this part includes tobacco smoke that drifts into any residential unit a person rents, leases, or owns, from another residential or commercial unit. [There is no mention of wood smoke or opacity in the nuisance provisions of the Utah Code.]

MODEL ORDINANCE

California Bay Area model ordinance

No person shall cause or allow a visible emission from any wood-burning device in any building or structure that exceeds No. 1 on the Ringlemann Chart or 20 percent opacity for a period or periods aggregating more than three consecutive minutes in any one hour period. Visible emissions created during a fifteen-minute start-up period are exempt from this regulation.

CITIES AND COUNTIES

Albuquerque, NM

* Certified wood heaters may be operated during a no-burn period provided that no visible emissions are produced after a twenty (20) minute period following start up or refueling.
* During a period in which the Director has not declared a no-burn, no person shall operate a solid fuel heating device in a manner which produces emission into the atmosphere if the emissions exceed 30 % opacity twenty (20) minutes or longer after ignition or refueling of the solid fuel burning device. Visible emission opacity shall be determined by an observer certified by the Director.

Amherst, MA

Smoke shall not exceed an average of 20% opacity for any 2-minute period during an hour or average of 40% for 6 minutes after start-up.

Davis, CA

The emission into the open air of visible smoke from any residential indoor non-wood pellet-burning appliance or any non EPA-Phase II certified wood burning appliance or fireplace used for home- heating purposes in such manner or in such amounts as to endanger or tend to endanger the health, comfort, safety or welfare of any reasonable person, or to cause unreasonable injury or damage to property or which could cause annoyance or discomfort in the area of the emission, is prohibited.

Eugene, OR (2021)

* During a green or yellow advisory, no person in charge of property shall operate or allow to be operated a solid-fuel space-heating device which discharges emissions that are of an opacity greater than 40 percent. This provision does not apply to the emissions during the building of a new fire, for a period or periods aggregating no more than ten minutes in any four-hour period.
* Upon a determination that a person has violated section 6.255 of this code, the city manager may impose upon the violator and any other person in charge of the property, an administrative penalty not greater than $500.

Fort Collins, CO
* After the first 15-minutes of start-up, smoke from the chimney must be at or less than 20% opacity (smoke should be barely visible looking at it with your back to the sun).
* Violation of City Code can result in a summons to appear in municipal court resulting in a fine of up to $1,000 and 180 days in jail.

Juneau, AK (2008)

No person may operate a solid fuel-fired heating device in such a manner that visible emissions reduce visibility through the exhaust for more than 15 minutes in any one hour by 50% opacity or greater.

St. Louis, MO (2021)

"The emission or escape into the ambient (outside) air within the City from any source or sources whatsoever of smoke, ashes, dust, soot, cinders, dirt, grime, acids, fumes, gases, vapors, odors, or any other substances or elements in such amounts as are detrimental to, or endanger the health, comfort, safety, welfare, property, or the normal conduct of business shall constitute a public nuisance, and it is considered unlawful for any person to cause, permit, or maintain any such public nuisance.  The Commissioner of Health and or his or her designee operating as Delegated Agents of the State of Missouri, may give additional consideration to the presence of emissions that cause severe annoyance or discomfort, or are offensive and objectionable to a significant number of citizens as determined by the Commissioner of Health and or his or her designee within the City of St. Louis Department of Health."

Vancouver, WA

* State law limits the density of smoke from indoor fires to ensure that people use clean burning techniques. This requirement is called the 20 percent smoke opacity limit. Opacity means how much your view through the smoke is blocked.
* 100 percent opacity means you can't see anything through the smoke. 20 percent opacity means there is very little smoke and you can see almost perfectly through it. If you use dry enough fuel, the right equipment, and give your fire the right amount of air, there should be no visible smoke from your chimney or stove pipe--only heat waves.
* There are two exceptions to the opacity rule which allow you limited time for denser smoke:
• Starting the fire. You have up to 20 minutes every four hours.
• Stoking the fire. You have up to six consecutive minutes in any one-hour period.