Wood is the most widely available and least expensive biomass fuel available. Burning firewood produced on one's own has the lowest carbon impact of all forms of wood burning and therefore can be considered the most sustainable form of wood burning. Boiler owners who produce their own firewood as a byproduct of managing their woodlots will also realize the greatest savings and cross benefits. Firewood is normally sold in units called cords. A cord of wood is a neat stack measuring four feet wide by four feet high and eight feet long. The heat content of a cord will vary depending on the species of wood. A cord of mixed softwood will have a heat value of 17 or 18 million BTU and a cord of mixed hardwood will have a heat value of 20 to 29 million BTU. By way of comparison a gallon of No. 2 fuel oil has a heat value of 140,000 BTU per gallon and propane has 93,000 BTU per gallon. Please use our fuel cost comparison tool to calculate the relative fuel costs in your area.
Wood Pellet fuel is manufactured from milled wood particles including waste wood and, less commonly, bark, which are pressed through dies at very high pressure. The most commonly available wood pellet fuel is graded "Premium". Premium wood pellet fuel contains less than 1% ash and conforms to other important limits. Typically wood pellets contain less than 4% moisture. Wood Pellets can be purchased in multi-ton bulk quantities or in 20 or 40 lb bags. As a rough approximation, 17.5 lbs of wood pellets provide the same amount of heat as a gallon of heating oil. With these characteristics, wood pellets burn very efficiently. They are also very easy and safe to transport and store. Wood pellets have an average net BTU rating of 8,200 BTU/lb.
Wood Chip fuel is produced by chipping whole trees or wood waste from forest management and land clearing. Wood Chips are less expensive than wood pellets. Wood chips come in various sizes, moisture contents, and qualities. When less bark and debris is included in wood chips will result in lower ash production during combustion. Whole tree chips like those produced by roadside chipping are usually not used in wood chip boilers producing under 2 MM Btus/hr. High quality chippers and chip screens are usually required to produce a maintenance free fuel chip. The Fröling T4 150 can burn a dry chip (Less than 30% moisture content). Moisture contents under 30% usually are achieved only by actively drying Eastern hardwoods. The European designation for permitted fuels for the T4 150 and are W20 or W30 for moisture and G30 or G50 for size. Wood chips (30% mc) have an average net BTU rating of 9,632,000 BTU/ton.