Twelve stoves are competing in the Wood Stove Decathlon and the nine independent judges give each stove a score of 1 – 10 in five different areas. The scores of the nine judges are averaged. The five scoring areas are equally weighted. The stove with the highest number wins.
Emissions. Particulate emissions or smoke is the hardest area to judge. The judges are using portable particulate matter analyzers that take samples of the smoke and provide a numerical amount of particles that are 2.5 milligrams or less. The judges will aim to test each stove 3 times and average the results because there can be a margin of error on any single test.
|Monday, Nov. 11: the tent goes up on the Mall|
Emissions samples are taken after the stove has started and warmed up in what is known as a “hot-to-hot” test. We do not test the emissions during the 20-minute start up phase, when emissions are the highest. Each stove is given wood that is the same moisture content (about 20%) and is loaded with about 12 pounds of wood per cubic foot of firebox volume.
Efficiency. Efficiency is measured using a “stack loss” method, meaning the temperature in the chimney is monitored to determine how much heat is being generated from the stove and how much is being wasted through the chimney. The higher the temperature coming out of the chimney, the lower the efficiency as this is heat that did not remain in the house. Stoves use many ways to extract heat before it goes up the chimney. Exhaust gases cannot get too low without an exhaust fan, because smoke would not be hot enough to rise, and moisture would condense. The highest recorded efficiencies in EPA certified wood stoves are 83%, using high heat value (HHV). Europeans use low heat values (LHV), which explains why you see numbers in the high 80s and low 90s in their wood stoves.
Innovation. This is a more subjective area of scoring by the judges, each of whom may give higher priority to certain kinds of innovation. Generally, judges are looking for new technology or components that are not standard on existing wood stoves. Judges will be looking for how “idiot proof” the stove is, meaning how it reduces opportunities for operator error, which can be significant in stoves with manually operated air controls. Judges will also be looking for how well a stove may be able to reduce emissions upon start up, mitigate the problem of using unseasoned wood and tackle many other common issues that wood stoves face.
Affordability. Judges are looking for stoves that are affordable to the average American family and will assess the cost of components of the stove and retail price, if there is one. Judges may also consider lifetime cost, and give higher marks to stoves that have longer lifespans or stoves that have lower installation costs. Operating costs are mainly reflected in the efficiency scoring area.
Consumer appeal. Judges will try to assess which stoves will be most attractive to buyers and have a greater chance of wide deployment. Features that do not impact emissions, efficiency or even affordability could score points in this area. Ease of use is important here, and a stove that recharged a cell phone or powered lights could gain points here, as could a variety of aesthetic attributes.