Government Regulation
Choosing the Right Indoor Equipment
Outdoor Wood-Fired Boilers
Burning Efficiently & Cleanly
Additional Resources


A wood fire can give your home a warm, cozy feeling, and in some cases can save you money. It can also affect air quality both indoors and out.

In many parts of Massachusetts, smoke from wood burning is a significant contributor to air pollution. Wood smoke contains toxic carbon monoxide, smog-causing nitrogen oxides, soot, fine particles, and a range of other chemicals and gases that can cause or worsen serious health problems, particularly among children, pregnant women, and people with breathing difficulties.

Fireplaces, indoor wood stoves, and other indoor wood-burning appliances can also bring harmful pollutants into your home if they are improperly installed, are loaded with too much fuel, have back drafts, or vent to chimneys or stovepipes that are cracked or in disrepair. Proper installation and venting to the outside are important.

Government Regulation

Some towns and cities use zoning and other laws to impose restrictions on wood-burning appliances. Some ban or limit them in new construction. All local fire departments and boards of health in Massachusetts have the authority to regulate outdoor burning and the nuisance conditions that can result.   Note: Municipalities adopting regulations to control air pollution need to comply with the provisions of M.G.L. Chapter 31C.  See: Guidance for Adopting Municipal Air Pollution Regulations Under M.G.L. Chapter 111, Section 31C  pdf format of Guidance: Adopting Municipal Air Pollution Regulations
doc format of                             Guidance: Adopting Municipal Air Pollution Regulations

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.  In December 2008, MassDEP also began specifically regulating the sale, installation and operation of outdoor hydronic heaters (wood-fired boilers) within the state.

On the federal level, the U.S. Environmental Protection Agency (EPA) has adopted emission standards and certification criteria for free standing indoor wood stoves and fireplace inserts with air supply controls and tight-fitting doors.  

Choosing the Right Indoor Equipment

In addition to the classic fireplace, there are many different types of wood-burning appliances on the market. Some pollute significantly less than others. Whether you are buying one for the first time or want to upgrade one you already own, choosing the right equipment can make a positive difference for the environment and in your home heating budget.

Since 1988, all indoor wood stoves and fireplace inserts sold in the United States have been subject to U.S. Environmental Protection Agency (EPA) emission standards. EPA-certified units feature baffles or dampers, secondary combustion chambers, and/or secondary air supplies to improve combustion efficiency and reduce emissions. They use less wood to produce the same amount of heat, saving you money while reducing air pollution.

If you own a pre-1988 indoor wood stove, fireplace insert, or other wood-burning appliance, you can significantly reduce its emissions by adding a catalytic combustor or converter. Similar to the unit found in your vehicle's emissions control system, it will help burn gases, fine particles and soot before they are vented outside, for a cleaner, more efficient wood fire. Catalytic units should be inspected at least twice per year, both before and during peak home heating season.

EPA periodically offers financial incentives to homeowners for replacing old wood stoves with EPA-certified units or non wood-burning heaters.

Outdoor Wood-Fired Boilers

Given the high costs of oil and natural gas, a growing number of people in Massachusetts and elsewhere across the country are looking at outdoor hydronic heaters (wood-fired boilers) as potential money-saving solutions for heating their homes. These units are typically located outside the buildings they heat in small, insulated sheds with short smokestacks (usually no more than six to ten feet tall). They burn wood to heat water that is piped underground to provide heat and hot water to occupied buildings.

Outdoor wood-fired boilers can be substantially dirtier and less efficient than other home heating technologies. An investigation by the New York State Attorney General's Environmental Protection Bureau found that even when used properly, one of these units can emit as much fine particle pollution as:

  • 2 heavy-duty diesel trucks
  • 12 EPA-certified indoor wood stoves
  • 45 passenger cars
  • 1,000 homes with oil heat
  • 1,800 homes with natural gas heat

NESCAUM, the Clean Air Association of the Northeast States, has also completed an Assessment of Outdoor Wood-Fired Boilers.

With their large, smoldering fires and short smokestacks, outdoor wood boilers create heavy smoke and release it close to the ground, where it lingers and exposes everyone in the area to nuisance conditions and health risks. Although these units are designed to burn dry, seasoned wood, some people use them to burn green wood, which generates much more smoke, and even household trash or construction debris, which not only can release a harmful array of chemicals but is also against state law.

Under MassDEP regulations issued in December 2008 ( 310 CMR 7.26(50) through (54): Wood-Fired Boilers  pdf format of 310 CMR 7.26(50) through (54): Wood-Fired Boilers
doc format of                             310 CMR 7.26(50) through (54): Wood-Fired Boilers                ):

  • Only those outdoor hydronic heaters that met EPA emission standards and whose manufacturers have filed compliance certifications with MassDEP may be sold for installation in the state. See: Massachusetts-Certified Outdoor Hydronic Heaters
  • New units must be located minimum distances away from property lines and neighbors' dwellings (determined by their heat output ratings and specific uses), meet minimum smokestack height requirements, burn only clean seasoned wood, and cause no nuisances or conditions of air pollution.
  • Like new units, existing units are subject to minimum smokestack height requirements, must burn only clean seasoned wood, and may not cause nuisances or conditions of air pollution.
  • Along with MassDEP, towns and cities - through their building, health, police and fire departments - are authorized to enforce specific provisions of the outdoor hydronic heater regulation. Some municipalities have enacted by-laws or ordinances that prohibit or limit the use of outdoor wood-fired boilers.  

Even when units are operated according to manufacturers' instructions, they can sometimes create nuisance conditions that are prohibited by state air quality regulations. MassDEP and local boards of health have taken enforcement actions against people who own and operate units that have caused excessive odor or smoke. Regardless of how much a unit might have cost to install, sometimes the only way to resolve the nuisance conditions an outdoor wood boiler creates is to stop using it permanently.

If you are thinking about buying an outdoor wood-fired boiler, first check to be sure it is legal to install and operate one in your community, and if so, whether there are any specific restrictions you need to know about. Second, consider the impacts an outdoor wood-fired boiler could have on your neighbors and their property. Finally, if you do purchase a unit, never use it to burn anything other than dry firewood, and to the extent you can, operate it only during the cold weather months

Burning Efficiently & Cleanly

How you operate and maintain your wood-burning appliance determines its combustion efficiency and the amount of air pollution it produces. Here are some tips for reducing the health risks and environmental impacts of burning wood to heat your home:

  • Use small pieces of split wood that have been dried and seasoned for at least six months.
  • Fuel your fire evenly but not excessively, since larger smoldering fires pollute the air more than smaller hot fires do.
  • Leave enough room in the firebox for air to circulate freely around the wood.
  • Never burn garbage, trash, treated woods or other highly polluting materials.
  • Have your wood-burning appliance and chimney or stovepipe inspected and cleaned on a regular basis.

Additional Resources