Impacts of wood species and moisture content on emissions from residential wood heaters

ABSTRACT

Homeowners burn wood of a wide range of species and moisture content (MC) in residential cordwood and pellet stoves. An effective emission certification test protocol must account for and accurately measure the impact of those variables in order to ensure a reasonable correlation between laboratory results and in-use emissions and to promote the design and manufacture of cleaner burning appliances. This study explored the effect of wood species and MC on emissions and efficiency in four cordwood and four pellet stoves. PM emissions were consistently lower with pellets manufactured from softwood than for hardwood species and were highly correlated with ash content. Higher MC oak fuel substantially increased PM emissions in a non-catalytic cordwood stove; however, a hybrid cordwood stove was able to meet federal emissions limits even with the higher MC fuel. The results of this study, in combination with previous research, suggest that certification tests that use softwood fuel likely report lower emissions than tests that use hardwood. Requiring hardwood and higher MC cordwood fuel in certification tests would enable the assessment of an appliance’s ability to operate well even when fuel conditions are not optimized.

Implications: The emission testing results reported in this paper call into question the adequacy of the fuel moisture content and fuel species specifications in testing protocols approved for certifying compliance with EPA’s New Source Performance Standards for cordwood and pellet stoves. We recommend changes in those specifications, including the prohibition of testing with Douglas fir and other low ash softwood species, requiring the use of cordwood test fuel with a higher moisture content, and requiring pellet stoves to be tested using hardwood pellets. Adoption of these measures would increase the replicability of tests. allow for the identification of stoves that are unlikely to perform well in the field when fuel conditions are not ideal, and, ultimately, result in the design of cleaner burning stoves.

Acknowledgment

The authors thank Dr. Ellen Burkhard, NYSERDA Project Manager and Dr. Thomas Butcher, Brookhaven National Laboratory for helpful comments throughout the project. The opinions expressed in this report do not necessarily reflect those of NYSERDA or the State of New York. Mention of product manufacturer names or trademarks does not imply endorsement by NESCAUM or NYSERDA

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data that support the findings of this study are available from NESCAUM upon reasonable request to NESCAUM’s Executive Director.

Additional information

Funding

This work was supported by the New York State Energy Research and Development Authority [Agreement #123059].

Notes on contributors

Barbara Morin

Barbara Morin is an Environmental Analyst at NESCAUM.

George Allen

George Allen is the Chief Scientist at NESCAUM.

Arthur Marin

Arthur Marin is the former Executive Director of NESCAUM.

Lisa Rector

Lisa Rector is a Policy and Program Director at NESCAUM.

Mahdi Ahmadi

Mahdi Ahmad, Austin, TX, is a NESCAUM consultant.