Some wood-burning stoves make it easier to burn fuel by using a chemical process which decreases the formation of pollutants. This process is called catalytic combustion. A wood stove catalytic combustor is comparable to a catalytic converter in a car. Inside the stove, the smoky exhaust passes through a coated honeycomb (the catalyst). The device is chemically coated with a metal that reacts with smoke and other combustion byproducts. These byproducts then generally burn at around 500 degrees, much lower than a non-catalytic stove, which needs a temperature of 1100 degrees. This allows users to burn cleaner at low burn rates, resulting in less wood consumption and overall higher efficiency. Efficiencies average around 78% (with a range of 63- 84%) using the higher heating of fuel (HHV).
Note that a catalyst stove burns more cleanly at lower burn rates. At high burn rates the particulate matter passes through the catalyst more quickly, with less retention time, resulting in higher emissions.
Catalytic stoves are typically more expensive long term than non-catalytic models because the catalyst honeycomb eventually breaks down and needs to be replaced. Modern catalysts can last up to 10 years with proper maintenance and use.
Non-catalytic or secondary combustion stoves make up about 80% of the market. They tend to be less expensive and have an average efficiency of 71% (with a range of 60-80%). Modern model design improvements like firebox insulation, a large baffle to produce a longer hotter gas flow path, and pre-heated combustion air which comes through small holes above the fuel in the firebox create lower emissions. The actual fire and the flames are generally more visible compared to a catalytic stove. Non-catalytic stoves are simpler to operate, and don’t require catalyst maintenance or cleaning.
A hybrid unit has both a catalyst and secondary combustion, so emissions are reduced from both low and high burns. Some hybrid stove manufacturers allow you to choose which technology you want to use (i.e., secondary combustion, the catalyst or both) at any given time. For example, if homeowners want to maximize heat output and don’t need to see the fire, they can set the stove to catalyst use only. If they want both heat and a view of the fire, they can choose the secondary combustion technology.