In general, the greater the dry weight of a non-resinous wood, the more heat it will give out when burned. Woods having high fuel values are osage orange, locust, hickory, oak, apple, black birch, yellow birch, hard maple, beech, long-leaf pine, and cherry. One cord of wood such as the above, weighing when dry about 3,500 to 4,000 pounds, is required to equal the heating value of one ton of coal. Of other woods, such as ash, black walnut, short-leaf pine, hemlock, red gum, sycamore, or soft maple, which weigh about 2,500 to 3,400 pounds a cord, it requires about a cord and a half to equal one ton of coal, while of wood such as Norway pine, cypress, basswood, spruce and white pine, two cords weighing when air dry 2,000 to 2,500 pounds each are required.
The available heat value of a cord of wood depends upon the extent to which it has been dried. If the wood is green part of the heat is taken up in evaporating the water. Therefore the drier the wood, the greater is the available heat.
A cord of wood occupies 128 cubic feet of space. If air spaces between the sticks are large, if the sticks are of small diameter, finely split, or twisted and knotty, or if the wood is loosely stacked, less wood is secured in a cord. If necessary to burn wood in a stove or furnace intended for coal, it may be done by covering the grate partly with sheet iron in which holes have been punched, or with fire brick, in order to reduce the draft. If this is not done the wood is wasted by being consumed too fast, producing a hot fire which may damage the fire-box.
Hickory is generally first choice among the non-resinous woods, because of the high fuel value to a unit volume of wood, even burning, and lasting quality. White oak is next, followed by black locust, hard maple, beech, birch, and " white ash." The white pines have a relatively low heat value, but ignite readily and give out a quick hot flame.