Highest-Efficiency Wood Stoves

High-Efficiency Designs

• The basic idea behind all high-efficiency wood heating stoves is to burn smoke particles to extract additional heat rather than letting them go up the chimney. High-efficiency stoves follow one of two basic designs. The highest-efficiency stoves use either a catalytic combustor or a secondary combustion chamber, coupled with a hot fire. The EPA limits smoke particle emissions for a catalytic wood stove to 4.1 grams per hour, while secondary combustion stoves are limited to 7.5 grams of smoke particles per hour. Smoke emissions from a low-efficiency stove can exceed 15 grams per hour. Stoves that meet EPA emission standards will have EPA compliance labels.

Catalytic Combustion

• Catalytic stoves place a ceramic honeycomb coated with a platinum alloy catalyst in the smoke path. As smoke from a hot fire rises up through the catalyst, the element triggers additional combustion of the smoke particles. Catalytic stoves have a bypass damper that the operator opens to allow smoke to escape without passing through the catalyst. You do this when starting the fire or reloading the stove to avoid fouling the catalyst. When the fire is hot enough, you close the bypass damper and let the catalyst work. Catalysts can last as little as two years or as long as six, depending on how you fire and maintain your stove.

Secondary Combustion

• Non-catalytic stoves use a secondary combustion chamber separated from the main firebox by a shelf-like baffle above the firebox. Smoke enters the secondary chamber at the front of the firebox, where it mixes with secondary combustion air drawn in from a vent behind the insulated back of the main firebox. The additional oxygen ignites secondary combustion of the smoke particles, releasing more heat. The high heat of secondary combustion will, over several years, cause the baffle to deteriorate, requiring replacement.

Right Size

• Your high-efficiency stove should be sized to fit the heating needs of your home. A rule of thumb is that your stove needs to put out 30,000 British thermal units of heat for each 1,000 square feet of floor area. People who buy a stove that’s too big tend to build low, smoldering fires to avoid overheating, but this practice thwarts the burning of the smoke that makes the stove an efficient heater and contributes to creosote buildup in the chimney. High-efficiency stoves need a hot fire, in excess of 1,100 degrees Fahrenheit, for complete combustion of fuel and smoke. A hot fire also means minimal creosote buildup.