A basic BTU chart lists the weight of a cord, which is 128 cubic feet, of wood and the heat energy in British Thermal Units produced by burning it. A BTU chart for firewood details the weight, burning characteristics, heat content and quality of different types of wood.
Different species vary in how quickly they burn and how hot the fire becomes. A BTU chart is useful for wood heating and selecting the most efficient wood available.
The weight of a cord is important because a wood with greater density produces more energy than a cord of wood with a lower density. Oak, ash and hard maple are commonly available and produce more heat than many other woods. Some BTU charts include data on both green wood and dry wood. Because green wood contains a lot of water, it does not produce as much heat energy.
Firewood BTU charts vary based on the test sample. Since there are gaps between the logs of wood in a cord, the actual volume of a cord varies, which may cause differing results between charts. The growing conditions impact the quality of the wood, and a lower-grade tree does not necessarily burn with the same qualities.