As the name suggests, pellet stoves burn "pellets." These actually are recycled sawdust, wood shavings, corn, walnut and peanut shells, and similar biomass wastes that are ground up, compressed, and extruded.

The 3/8-inch to 1-inch-long pellets look like rabbit feed, and they're sold in manageable 40-pound bags. Some pellet stoves are also designed to burn corn kernels, nutshells, and wood chips. Pellets and related fuels turn wastes that would otherwise be dumped at landfills into energy, lessening our dependence on oil.

Both because of the fuel's consistency and because of the stove's combustion mechanics, pellets burn very hot. This means they burn more efficiently and more cleany than wood.

Intense compression squeezes the moisture out of pellets, dropping their moisture content to below 8 percent, which is very dry compared with cord wood, which has from 20 percent to 30 percent moisture.

The drier the fuel, the more heat it can produce. And the high-temperature fire burns more of the fuel. Compared with EPA-certified wood stoves that give off about 5 grams of particulates per hour, pellet stoves have very low particulate emissions, some far less than 1 gram per hour.

Combustion efficiency is a measure of how much of a fuel is converted to energy by an appliance. Pellet stoves offer 75 percent to 90 percent overall efficiency (be sure to look for "overall efficiency" when comparing). In fact, so much heat is extracted that most pellet stoves may be vented horizontally out through a wall instead of through a conventional chimney (see How a Pellet Stove Works).

Pellets also create much less ash than cord wood and give off far less creosote, a common wood stove and fireplace hazard that blackens glass doors and collects in chimneys, causing chimney fires.

More about Pellet Stoves:

• Pellet Stoves Buying Guide
• Comparing Pellet Stove Energy Costs
  
• How a Pellet Stove Works
  

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