Outdoor Wood-Fired Boilers and Air Quality
Environmental and Health Concerns

Background

Over the past few years, the use of outdoor wood boilers (OWBs) to provide heat has increased in New Hampshire and throughout the Northeast region, primarily as a result of rising fuel costs. Unfortunately, these devices are often more polluting and less efficient than other home heating devices. Unlike other residential wood burning devices such as indoor wood stoves and pellet stoves, OWBs are not required to meet federal emission standards and are not yet EPA-certified. They can create heavy smoke that may impact your health and that of your family and neighbors, and they may also be a nuisance and harm the environment.

What are Outdoor Wood Boilers?

OWBs, also referred to as outdoor wood furnaces or outdoor wood-fired hydronic heaters, are free-standing wood burning devices that heat water, which is then pumped to one or more structures to provide heat. They resemble a small shed or mini-barn with a short smokestack on top. OWBs may be used to heat homes and buildings, produce domestic hot water, heat swimming pools or hot tubs, and provide heat to agricultural operations such as greenhouses and dairies. Many OWBs are used in rural, cold climates like New Hampshire where wood is readily available.

Source: Hearth, Patio and Barbeque Association (from US EPA website)

The Problem: Outdoor Wood Boilers Produce Air Pollution

Current OWBs are often dirtier and less efficient than other home heating devices. With smoldering fires and short smokestacks (usually less than 12 feet tall), OWBs often release heavy smoke close to the ground, where it creates a nuisance and is unhealthy to breathe. Smoke from OWBs contains emissions of fine particle pollution, carbon monoxide, and other organic products formed from incomplete combustion, such as formaldehyde, benzene and aromatic hydrocarbons.

When inhaled, fine particles from smoke emissions are carried deep into the lungs and can aggravate existing medical conditions such as asthma or lung and heart disease, as well as impair lung function. Exposure to other pollutants in smoke, such as benzene or polycyclic aromatic hydrocarbons, can cause a diverse range of harmful health effects, including asthmatic sensitivity, lung illnesses and cancer.

The health problem is compounded when people burn inappropriate materials. While OWB units are designed to burn dry, seasoned wood, some people burn green wood which is less efficient and generates much more smoke. Additionally, because of their oversized fireboxes, there is concern that some OWB users may illegally burn materials such as tires, household garbage, and construction debris. Burning these materials produces additional toxic and hazardous air pollutants.

While wood is a renewable resource and can be “global warming neutral” when harvested in a sustainable manner, these attributes are negated if people use devices like OWBs that are inefficient and produce significant amounts of air pollution.

A Solution: Buy a Cleaner OWB or Use an Alternative Heating Source

Before buying an OWB, you should consider the resulting health and environmental impacts to your family and neighbors and think about different alternative heating systems that are cleaner and more efficient. One alternative might be an indoor wood stove. EPA requires all indoor wood stoves manufactured after the late 1980s to be certified to meet air emissions standards.

In the absence of federal regulation of OWBs, some local, state and regional organizations are establishing emissions standards and prohibiting the sale or installation of any unit that does not meet the standards. In 2007 at the federal level, EPA initiated a voluntary partnership with manufacturers to produce and sell cleaner, more efficient OWBs that meet a certain performance level. As of early 2007, ten manufacturers had signed an agreement with EPA to make cleaner models available to consumers – ones that are about 70 percent less polluting than existing models!

If you choose to buy an OWB, you should look for the cleanest models available. EPA’s voluntary program uses a labeling program to identify the “cleaner” units and to show how they compare to EPA’s performance specifications (see sample label).

EPA also provides information to buyers regarding proper operation and maintenance of the units, including what is allowed to be burned.

Tips to Reduce Air Pollution from Existing OWBs

If you already own an OWB, to decrease its harmful health and environmental affects, you should ensure that it is properly installed, operated, and maintained according to the manufacturer’s instructions. Here are a few best management practices to follow:

• Have the unit installed by a professional.
• When determining where to locate an OWB, take into consideration how close the unit is placed in relation to neighboring properties, especially neighboring residences. Be aware of the direction of prevailing winds and of the contours of the land. In New England, recommended minimum distance setbacks from property lines range from 50 to 500 feet.
• Follow local ordinances, manufacturers’ recommendations, and best practices for stack heights and setbacks from property lines or structures.
• Never start a fire with gasoline, kerosene, charcoal starter, or a propane torch.
• Burn only dry, well-seasoned wood that meets the definition of “clean” wood. Never burn wet, rotted, diseased, or moldy wood.
• Never burn household garbage, cardboard or coated, painted, or pressure-treated wood.
• Keep the doors of the unit closed unless you are loading or stoking the live fire.
• Regularly remove ashes from the OWB into a metal container with a cover and properly cool before disposing.
• Conduct yearly maintenance for safety reasons. EPA and fire officials recommend that your OWB, chimney, and vents be professionally inspected and cleaned, if necessary, each year to keep them in safe working order.

Finally, you should consider replacing your existing older OWB with a cleaner, more efficient heating system.

For More Information

Information about OWBs and EPA’s voluntary program, including the health effects of OWBs and a list of cleaner, more efficient models, can be found at www.epa.gov/woodheaters.

Information about local and state actions to address OWBs in the Northeast, including model regulations, can be found at http://www.nescaum.org/topics/outdoor-hydronic-heaters.

For general information on OWBs in New Hampshire, contact the DES Air Resources Division at (603) 271-1370.