OLR Research Report

February 29, 2008




By: Paul Frisman, Principal Analyst

You asked about states' regulation of wood smoke. Regulations concerning wood smoke pollution vary by source. This report examines the regulation of smoke produced by wood stoves and outdoor wood burning boilers and the regulations on the burning of construction and demolition (C&D) waste.


The U.S. Environmental Protection Agency (EPA) regulates the emission of particulate matter, or soot, from indoor wood stoves, but does not prohibit states from adopting stricter standards. Only Washington state appears to have a stricter standard. EPA does not regulate outdoor wood boiler (OWB) emissions, but a few states, such as Maine and Vermont, limit their soot emissions, or are considering such regulation. Some states, such as Connecticut, regulate the opacity (density) of OWB smoke, where OWBs can be located, and the height of their smokestacks.

The New England states regulate the individual pollutants emitted by the burning of C&D wood debris.


Wood smoke contains a complex mixture of gases and soot particles. The gases include carbon monoxide, nitrogen and sulfur oxides, volatile organic compounds, and others associated with deleterious health effects. The soot particles (also called particulate matter or PM) are small enough to enter a person's lungs, and can lead to serious respiratory problems.


The EPA defines wood stoves as freestanding devices used to burn cordwood to heat a specific room or zone of a house. The definition includes fireplace inserts, which are woodstoves installed in existing fireplaces.

Since 1990, the EPA has required all wood stoves to meet certain emission limits. Stoves with catalytic converters (devices that reduce emissions toxicity) must be designed to emit less than 4.1 grams per hour of particulate matter; stoves without catalytic converters must be designed to emit a maximum of 7.5 grams per hour. EPA certified stoves are labeled as such.

According to NESCAUM, a nonprofit association of air quality agencies in eight northeastern states, Washington is the only state to impose stricter wood stove standards than the EPA. Washington limits emissions to 2.5 grams per hour for catalytic models and 4.5 grams per hour for non-catalytic models (Washington Administrative Code 173-433-100(3)).

Since 2005, EPA has worked with gas utilities and wood stove manufacturers, distributors, and retailers to support campaigns in which consumers receive financial incentives to replace older stoves with non-wood burning equipment (gas stoves), or EPA-certified wood stoves. EPA-certified stoves emit about 70% less pollution than older models. EPA reported in 2006 that about 10 million wood stoves were in use. Of these, between 70% and 80% are older, more polluting wood stoves. More information on these campaigns, as well as individual case studies, is available at


An OWB, also known as an outdoor wood-burning furnace or hydronic heater, is essentially a wood-fired boiler in a small, insulated shed with a smoke stack. It heats water that is carried through underground pipes to heat a home or building, domestic hot water, a swimming pool, Jacuzzi, or hot tub. The popularity of OWBs has increased as the cost of oil and gas has risen. Unlike wood stoves, their emissions are not regulated by EPA. (In 2006, EPA estimated it would take between five to seven years to implement a federal OWB standard.)

A number of studies have found that OWB emissions pose a health threat. According to “Smoke Gets in Your Lungs,” an October 2005 report from the New York attorney general's office, OWBs “may be among the dirtiest and least economical modes of heating, especially when improperly used.”

Even when used properly, the report stated, OWBs emit about four times as much fine particulate matter (PM 2.5) as conventional wood stoves, about 12 time as much as EPA-certified wood stoves, 1000 times more than oil furnaces, and 1,800 times more than gas furnaces. The health effects of OWBs emissions are made worse, studies state, because, (1) unlike wood stoves, they are often operated year-round, (2) their design “encourages burning of inappropriate materials,” such as refuse, tires, wood waste, and railroad ties, and (3) their relatively short smokestack height allows smoke to travel to neighboring buildings.

States have taken several approaches in regulating OWBs. A number of states, including Connecticut, have implemented setback and stack height requirements for OWBs. Connecticut also requires that OWB operators burn only wood that has not been chemically treated (CGS 22a-174k). The Connecticut law applies only to OWBs installed after July 8, 2005. OWBs installed or operated before that date are not subject to these restrictions.

States also can regulate use of OWBs and other smoke-generating sources through smoke opacity (density) regulations, although the transient nature of smoke emissions may make these hard to enforce. Zero percent opacity means no smoke is visible; 100% opacity would be smoke too thick to see through. Connecticut's opacity limit is an average of 20% during six consecutive minutes, or a 40% average for one minute.

At least two states, Vermont and Maine, have imposed emissions requirements, and a third, Ohio, is proposing doing so. (Vermont and Maine also restrict the types of fuels that OWBs can burn, and Ohio would do so.) A number of other states are considering model regulations NESCAUM proposed in 2007. Also in 2007, EPA and a number of OWB manufacturers voluntarily agreed to produce cleaner devices.

Finally, some municipalities, such as Hebron, Connecticut; Hampden, Massachusetts; and Watertown, New York, have banned them.


NESCAUM issued its model regulations on January 29, 2007. They can be found at NESCAUM's website ( Among other things, the regulations propose emissions limits for residential OWBs of 0.44 pounds per million British Thermal Units (lb./mmBTU) starting April 1, 2008, and 0.32 pounds per million BTUs starting April 1, 2010. (A British Thermal Unit or BTU is a unit of energy. One BTU is the amount of heat needed to raise the temperature of one pound of water by one degree Fahrenheit). The model regulations also propose setback limits that vary according to the OWB's emissions rate, prohibits people from operating them between April 15 and September 30 unless they meet the emission limits, and limits the types of fuel that can be burned.

State Emissions Requirements

Maine. As of April 1, 2008, no one can sell or distribute an OWB unless it meets a PM limit of 0.60 lb./mmBTU. Starting April 1, 2010, no one can sell or distribute an OWB unless it meets a PM limit of 0.32 lb./mmBTU (Code of Maine Rules, 06-96, Ch. 150).

Ohio. The Ohio EPA is proposing draft regulations that would set a two-phase emission limit for installation of new OWBs. Phase I would set a limit of 0.44 lb./mmBTU starting six months after the proposed rules take effect. Phase II would set a limit of 0.32 lb./mmBTU, and take effect July 1, 2010. In addition, the proposed rules would require OWBs to be installed at least 200 feet from a property line, with a stack at least five feet higher than the roof peak of any structure within 150 feet. It also would bar OWBs that did not meet the above emissions limits from being operated from April 15 to September 13 of any year (OAC Rule 3745-115-02). More information on the proposed Ohio rule can be found at

Vermont. As of March 31, 2008, all OWBs sold or distributed in Vermont must meet PM limits of 0.44 lb./mmBTU. Also by that date, the Agency of Natural Resources secretary must file a proposed rule to establish a PM limit of 0.32 lb./mmBTU (10 VSA 558).

State Siting Requirements

Connecticut. By law, OWBs built, modified or installed in Connecticut after July 8, 2005, must (1) be installed at least 200 feet from the nearest neighboring home, and (2) have a chimney shorter than 55 feet tall but at least as tall as the roof peaks of neighboring homes within 500 feet of the OWB (CGS 22a-174k).

Vermont. Vermont requires all OWBs to be located more than 200 feet from any home other than the one it serves. The OWB must have a stack that extends higher than the roof peak of the structure it serves if any other home is located within 500 feet of it.

Maine. Unlike the requirements in Connecticut and Vermont, Maine's setback requirements depend on the OWB's emissions. OWBs with PM emissions that exceed 0.60 lb./mmBTU must be at least 250 feet from the nearest property line. OWB's that meet emission limits of 0.60 lb./MmBTU must be installed at least 100 feet from the nearest property line. OWBs with emission limits of 0.32 lb./mmBTU must be installed at least 50 feet from the nearest property line. Regardless of its PM emission rates, no OWB may be installed closer than 500 feet from the property line of a state licensed school, daycare or health facility. Stack height requirements also vary by emission limits.

EPA and OWB Manufacturer's Voluntary Agreement

In 2007, EPA and a number of OWB manufacturers agreed on a voluntary program to produce cleaner OWBs. The cleaner models must emit no more than 0.60 lb./mmBTU. These heaters, which carry an orange tag, are 70% less polluting than other models.


According to a 2006 NESCAUM report, the use of biomass fuels, such as wood derived from C&D debris, has become more attractive as the cost of other types of fuel increases and states create incentives to use renewable energy sources. The report noted that facilities in Maine, Massachusetts, and New Hampshire have received permit applications proposing new wood-fired power plants. In Connecticut, PA 07-5 temporarily broadens the types of power plants where C&D waste and certain other biomass products can be used as a fuel, and the resulting power considered a class I renewable resource.

According to the NESCAUM report, the use of appropriately processed C&D wood is similar in its emission profile to that of virgin wood, and other fuels such as coal and oil. The report (attached), which also can be found at notes that it is likely that control requirements for plants burning this wood would be similar to, or more stringent than, those required for plants burning “clean” wood.

A critical element for use of C&D wood is the development of strict fuel standards. “The elimination of treated wood, such as chromated copper arsenate wood and pentachlorophenol-treated wood significantly reduces arsenic emissions,” the report stated. “Furthermore, fuel standards minimizing contamination from other C&D materials and removing C&D fine material from the fuel chips increases fuel quality substantially, resulting in lower metal and other air toxic emissions. Finally, requirements for comprehensive testing and sampling of the fuel at both the processing facility and the location of the end user will assure that the fuel quality is maintained.” (Pentachrophenol is a chemical used as a pesticide and wood preservative).

The Coalition of Northeastern Governors has identified 19 facilities nationwide that are permitted to burn waste wood as a fuel sources. Nine of these are in California, four are in Maine and three are in Michigan, with one each in Florida, Washington and Wisconsin.

Regional Air Emission Requirements

The NESCAUM report found that Connecticut, Maine, Massachusetts, New Hampshire, New York, Rhode Island and Vermont require the installation of Best Available Control Technology or Lowest Achievable Emissions Rate controls for criteria pollutants and compliance with air toxics limits for wood burning power generation.

Connecticut C&D Requirements

In Connecticut, processed C&D wood may be disposed of at a biomass gasification plant that qualifies as a Class I renewable energy source, a resources recovery facility, or at a permitted municipal solid waste landfill or any solid waste disposal area for which a permit has been issued for the disposal of bulky waste. By law, processed C&D wood means the wood portion of C&D waste that has been sorted to remove (1) plastics, plaster, gypsum wallboard, asbestos, or asphalt shingles; (2)

regulated wood fuel as defined by law; and (3) wood which contains creosote or to which pesticides have been applied or which contains substances the law defines as hazardous waste (CGS 22a-208x).

“Regulated wood fuel” is processed wood from construction and demolition activities which has been sorted to remove plastics, plaster, gypsum wallboard, asbestos, asphalt shingles and wood which contains creosote or to which pesticides have been applied or which contains substances defined as hazardous under section 22a-115 (CGS 22a-209a). Any one intending to remove or process wood from C&D debris for use as a regulated wood fuel must possess a DEP volume reduction permit. Only a regulated wood fuel user may burn regulated wood fuel. By law, these are biomass gasification plants or resource recovery facilities that burn more than 100 million BTUs per hour of the fuel for heat, light, power or energy (CGS 22a-209a(9)).