There is limited research or literature addressing the repeatability of test results from wood stoves, or the relationship between individual factors and overall repeatability. The French ecolabelling scheme, the Flamme Verte does organize round robin tests on a regular basis, where the same stove is circulated among their affiliated test labs. Taking OGC as one of the more volatile parameters the test results reported range from 29 to 122 mg/m3 with 92 mg/m3 for the declared values (a factor of x3 in spread).
SINTEF has reported relative standard deviation figures of the spread of test results when comparing the European method and the Norway (FFDT) method, suggesting that the Relative Standard Deviation (RDS) is somehow minor by the FFDT method. For a test at nominal heat output, sampling PM by the DIN Plus method, the RDS is 41% for the European method going down to 27% when sampling by the Norway method. A rough improvement of one third.
From the Danish ecodesign market surveillance activities in 2022 we saw poor reproducibility by the European test method, more so on the indicators of incomplete combustion than on efficiency and PM. Out of 15 stoves tested 11 failed on one or more parameters during the first unattended testing round. At a second testing round with presence of the manufacturer, we saw an improvement of reproducibility ranging from a few % for efficiency to 37% on OGC.
Increasing the number of consecutive combustion cycles from three to five will add significantly to improving reproducibility. By increasing the number of combustion cycles to five, the impact of any lucky punch cycle is balanced by the full set of five, yielding a more robust test result which is closer to the true values. It is the same basic idea behind any of the current fixed load cycle tests, the BeReal, the Blue Angel and the EU Real LIFE protocol.
Trying to aggregate the improvement potential of the recommendations is not an easy task since there is not much documentation available. But we can make some experience-based estimates which can at least indicate the combined effect of adopting these recommendations, bearing in mind that this is not science (see table below). This is just to say that the aggregated result indicating a relative improvement potential of 31%, might as well be 25% or 35%. Regardless, the figures demonstrate that there is a significant improvement potential to be harvested, some of it even in the form of low hanging fruits.