Wood smoke is unburned fuel, some of which accumulates in your chimney as creosote while the remainder exits the stack as smoke. The key to reducing air pollution from woodstoves is to burn fuel more completely.
The three main things that make a stove clean burning:
a. How it is designed.
b. How it is installed.
c. How it is operated.
Some stove manufacturers use catalytic combustors to burn fuel more completely while others use a variety of design features such as baffles, secondary combustion chambers, and introduction of secondary air.
EPA-certified stoves offer 70 to 90 percent reduction of particulate matter over the older conventional model stoves. This is based on laboratory testing.