A Critical Review and Discussion on Emission Factors for Wood Stoves

Abstract

Small scale heating appliances such as wood stoves, significantly contribute to domestic heating and energy security in many European countries. However, emissions from wood stoves remain a significant concern, even though modern wood stoves are continuously improved to reduce emissions due to incomplete combustion. Most State-Of-The-Art (SOTA) stoves after the 1990s, achieve significantly lower emissions than stoves produced in the period 1940-1990. The main reason being the introduction of emission limits and test standards both in Norway and other European countries. SOTA stoves today, including catalyst stoves and the more recent downdraft concepts, all apply a strategic and more or less optimized staged air supply. In stoves without catalyst, optimized air supply and combustion chamber geometry as well as combustion chamber insulation, are the main reasons modern stoves achieve better burnout. When comparing national emission inventories, we find unacceptable large variations in emission factors for most reported compounds in all official stove categories. There are in some cases plausible reasons for such differences, but for some cases the differences can hardly be justified. Both stove categories, old and new, suffers from differences of up to two magnitudes, when comparing emission factors used in the national emission inventories in the Nordic countries. Hence, there is a real need to correct and align these for inclusion in national emission inventories, which should be reflecting real-life emissions as accurately as possible. As stoves are continuously being improved, we also suggest yearly updates accounting for such improvements, in the annual national emission inventories reports.