Vermont cast iron stoves are EPA certified, which independent research assures a good standard of efficiency according to a 2014 Wood Heat Organization Inc. report. Vermont Castings claims their wood burning stoves radiate between 70 and 80 percent of available heat energy which makes them highly efficient.
More than 80 percent efficiency is generally considered undesirable for wood-burning stoves because the lack of heat in the flu creates a weak draft, which leads to inefficient evacuation of smoke as well as water condensation problems. When installing a wood burning stove it is vital that the flu and chimney also be properly installed. The most efficiently designed stove will only work well if the system can evacuate effectively.