2011 Aug. 5: American Lung Assoc. of the Upper Midwest: Regarding Residential Outdoor Wood Fired Boilers

2011 Aug. 5: American Lung Assoc. of the Upper Midwest: Regarding Residential Outdoor Wood Fired Boilers


As the price of home heating oil, natural gas and liquefied petroleum gas

increases, more households are looking towards heating alternatives. In growing numbers,

people are turning to wood-burning devices to replace oil and gas heating. Wood-fired devices

include masonry heaters, indoor wood stoves, indoor wood furnaces, pellet stoves and outdoor

wood-fired boilers (OWB). The recent increase in OWBs are of particular concern to state

environmental agencies because of the cumulative stack emissions from these appliances which

are greater than other wood burning appliances; and, unlike other wood burning devices, are

generally unregulated. Where once these OWBs were located mainly in rural areas, they are

now being used in suburban and urban neighborhoods to provide space heating, year-round

heating of hot water, and heating of swimming pools, Jacuzzis and hot tubs.

OWBs (also called outdoor hydronic heaters or outdoor wood furnaces) are free standing wood

burning appliances that heat water, which is then pumped to one or more structures to provide

heat. OWBs can also be used to provide hot water and to heat swimming pools, etc. Units are

typically the size and shape of a small storage shed, or mini-barn with a short stack on top and

are much larger in size and differ in design, operation and emissions when compared to smaller

indoor wood stoves, pellet stoves, fireplaces and barbeque pits.

OWBs operate on a cyclical operating pattern creating an on/off cycle. Manufacturers advertise

OWBs for use with wood fuel, but sometimes other types of fuel (such as wet, un-split wood,

wood waste, yard wastes, general refuse, tires and railroad ties) are used.

Operating Issues:

Due to the design and operating practices of the OWBs, some environmental

concerns can result. Unlike indoor wood stoves and fireplaces, OWBs generally operate year

round. The quantity of (black) smoke generated from OWBs is more significant than in other

wood burning appliances. The lower combustion temperatures and cyclic nature of opening and

closing dampers to regulate the unit creates fire smoldering, build-up of smoke and creosote.

Another contributing factor to this smoke is the short stack height of OWBs resulting in limited

vertical dispersion of the resulting emissions. Certain weather conditions aggravate the problem,

including cold weather inversions, when the smoke does not rise but stays close to the ground.

The large capacity of the fuel being used and the potential use of variable fuel also results in

adverse uncontrollable emissions. Lastly, the units do not have emission control equipment such

as catalytic control devices or secondary combustion chambers.

Public Health Concerns:

Wood smoke contains a complex mixture of airborne particulate

matter (PM) and gases, many of which have been known to produce acute and chronic biological

effects and deleterious physiologic responses to the exposed population.


Short and long-term exposure to airborne PM is associated with cardiopulmonary health effects,

including increased respiratory and cardiac symptoms, hospital admissions and emergency room

visits, and premature death. Other harmful health effects include aggravated asthma, decreased

lung function and chronic bronchitis. In areas where residential wood combustion was largely

used, a major source of ambient PM resulted in higher health risks

1. Over 50% of the population

falls into susceptible subgroups (children, asthmatics, persons with pre-existing respiratory

disease or cardiac problems, older adults, and healthy adults who work or exercise outdoors) that

are most affected by PM


Wood smoke includes numerous gases, including carbon monoxide, nitrogen and sulfur oxides,

volatile organic compounds (VOCs), poly aromatic hydrocarbons (PAHs) and chlorinated

dioxins. VOCs can cause upper airway irritation, headaches, and possibly cancer


American Lung Association of the Upper Midwest’s Position:

The American Lung Association of the Upper Midwest recognizes that pollution from the

combustion of wood and other biomass sources may pose a significant threat to human health,

and supports measures to transition away from using these products for residential heat


The American Lung Association of the Upper Midwest supports regulating how and when

OWBs can be used. This would include regulations for design and operation, emission

limitations and fuel usage.

The American Lung Association of the Upper Midwest calls for effective enforcement of

existing laws and regulations governing the use of OWBs, as well as the expanded regulation of

air pollution emissions from these sources.

The American Lung Association of the Upper Midwest recommends continuing research on the

health effects of burning wood and other biomass sources, and the technologies to reduce the

potential emissions associated with the combustion of these fuels.


Review of the National Ambient Air Quality Standards for Particulate Matter: Policy Assessment of Scientific and

Technical Information. EPA-452/R-05-005. U.S. EPA Office of Air Quality Planning and Standards: Research

Triangle Park, NC 2005.


Johnson PRS, Graham JJ. Fine Particulate matter national Ambient Air Quality Standards: public health impact on

populations in the northeastern United States.

Environ Health Persp 2005;113:1140-1147.


Pierson, WE,

This entry was posted in Opinion, OWB regulation discussion (statewide), OWB regulations. Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s