Wood stoves can be a wonderful way to provide extra warmth and comfort in cold months. The EPA is stepping up the monitoring of wood stoves and most models on the market today have ratings for grams of smoke per hour emitted (g/s). Wood stove manufacturers are required to label woodstoves with smoke and efficiency ratings so that consumers can compare models based on these factors.
Non-catalytic stoves offer three components to increase efficiency: large baffles which create hotter flow, increased firebox insulation and an inflow of preheated air through tiny holes in the firebox above the wood. These are relatively simple to operate, and keep in efficient working order, but do require maintenance for deteriorating baffles and other components from high heat burning. Non-catalytic wood stoves must emit 7.5 g/s or less to meet EPA guidelines.
Catalytic stoves are more complicated, but if used properly can create a long-term and efficient burn. The catalyst is a honeycombed ceramic unit, which provides a secondary and more complete burn of the smoke gases and particles. Like the non-catalytic baffles, the catalytic unit will need to be replaced as it too degrades over time, but can last up to six seasons with careful use. Catalytic Woodstoves must stay below a 4.1g/s to comply with EPA guidelines.
The EPA white rating sticker (below right) contains three pieces of information: smoke or grams per hour output; 
efficiency on a sliding scale between 50% and 100%; and output given in a range of BTUS per hour. The stove retailer will be able to assist in sizing the stove to suit the circumstances.
It should be noted that the fuel has an effect on how well and efficiently a stove works. Variables such as hardness and wetness can dramatically affect the performance of a woodstove. In general, most woodstove users prefer hard woods that have been seasoned at least two years to provide maximum heat and efficiency.