Wood pellets pack a lot of punch in a small package. Made of compressed sawdust, they burn cleaner than traditional firewood. That's because they contain less moisture—typically between 3 and 8 percent compared with 20 to 50 percent for firewood. What's more, they come in 20- and 40-lb. packages that are easier to store and transport than big stacks of cord wood. Burning pellets used to require a pellet stove, but New Hampshire-based Energex has created an add-on product, called Prometheus, that allows homeowners to convert any fireplace or wood-burning stove to pellets. The Prometheus is a steel basket with its sides and bottom covered by thousands of honeycomb-shaped airholes. This setup allows homeowners to use the clean-burning pellets. Four front-to-back channels on the unit divide the basket into sections, which allows combustion air to reach the middle of the fuel source; this ensures that all of the pellets burn. Baskets range in size from 10 to 26 inches and hold from 10 to 30 lbs. of pellet fuel. A fully loaded basket can burn unattended for 2 to 12 hours.