Synopsis: As fuel costs rise, homeowners are increasingly looking for more economical means of heating their homes. One increasingly prevalent option in recent years has been outdoor wood-fired boilers. These units consist of a structure sitting outside the home in which wood can be burned to heat a home’s boiler. Because the burning is done outside the home, the units are not subject to federal regulations limiting the emissions of in-home wood burning devices. As a result, most models on the market lack even the most basic emission controlling technologies or design features. Although studies of the emissions of these units are relatively few, the preliminary indications are that that these units emit considerably more than their regulated indoor counterparts. Complaints of smoke and odor from neighbors of those using these units have become commonplace and are a leading factor in a building emphasis to regulate or otherwise reduce the emissions of outdoor wood fired boilers.

In addition to smoke and particulate matter, it is very likely that these outdoor boilers are strong sources of many persistent toxic substances, including several that are important health concern in the Great Lakes basin. Such emissions could be particularly toxic if household waste is also burnt in these units, which has been suggested to be a common practice. Unfortunately, the Great Lakes states represent approximately 80% of the overall sales of these units and the rate of sales has been growing at an extremely fast pace over the past decade. It is therefore important to provide public health and natural resource protection officials within the Great Lakes region accurate and appropriate information regarding the levels of persistent toxic substances from these units. This study will use a controlled laboratory setting to examine the persistent toxic substance emissions from outdoor wood-fired boilers. The information will lead to an assessment of the relative importance of burning of wood and/or household trash in these units as a source of toxic substances in the Great Lakes.

Chemicals Studied: The study will examine the emissions of polychlorinated dibenzo-dioxins and furans (PCDD/Fs) and polycyclic aromatic hydrocarbons (PAH). PCDD/Fs are a class of highly persistent and toxic compounds formed from a wide range of combustion processes. Emissions of these compounds are particularly elevated when plastics are burned in combination with other materials. PAH are another class of toxic compounds emitted by combustion processes. Several of these compounds are found in elevated levels in sediments of the Great Lakes. Wood combustion is an important source of PAH emissions and the relatively uncontrolled emissions taking place in outdoor wood-fired boilers may be particularly high in these emissions. Other compounds may also be studied based on the findings of initial tests that will look for evidence of certain compounds.

Project Duration: The project began in the summer of 2007. The emissions testing, analysis and reporting of results should be completed by the summer of 2009.

Methods Used: Several styles of outdoor wood-fired boilers will be obtained and taken to an EPA laboratory designed for testing emissions from such items. Fuel, both wood and household waste, will be obtained and used in the combustion tests. A range of woods will be tested that are believed to represent the range of woods typically burned in these units. Initial tests will be conducted to determine the complete list of chemicals whose emissions will be studied. A comprehensive series of combustion tests will be done in the laboratory to characterize emissions from the boilers over a wide range of combustion conditions and with different wood and waste fuels. The results of these tests will be combined with other knowledge about the use of outdoor food-fired boilers to produce an estimate of emissions from these boilers within the region.

Potential Results and Implications: This project will provide essential information regarding the type and level of toxic emissions from a rapidly growing type of source. Improving the understanding of what emissions are produced by outdoor wood-fired boilers will help policy makers decide if and what actions may be appropriate to protect human health and the environment from such emissions. Such actions could include working with homeowners on understanding good burning practices and working with manufacturers of these boilers to incorporate design features that would reduce emissions.

Project Contact:
Sukh Sidhu
University of Dayton
Research Institute
300 College Park
Dayton, Ohio 45469-0104
Phone: (937) 229-3605
Email: sukh.sidhu@udri.udayton.edu