Keep in mind that rated efficiency is established under laboratory conditions and almost all actual use efficiencies are far lower. Woodburning Open fireplaces, even the Rumford design, are the least efficient space heaters. Also, due to incomplete combustion, open fires add greatly to pollution. One step in the right direction is the use of tight fitting fire doors and outside combustion air, but this will only lessen the amount of warm air wasted and will not affect emissions. Airtight woodstoves work by radiating heat from a cast iron casing.
Efficiency is far higher than open fires and emissions are reduced by half.
The recently developed advanced combustion wood stove does not use any air from the house and is far more efficient than previous models. Due to an elaborate burner arrangement exhaust gases are reignited so that emissions are greatly reduced. Electric fans supply air and circulate heat. Natural Gas Appliances Gas logs eliminate most of the emissions of wood burning, but even with glass doors they add little heat. There are also safety concerns when used in a retrofit unless the chimney is relined.